feat: per-board activity log

Adds an audit trail per board, visible from a new clock-icon button on the
toolbar. Useful for review-style work where someone wants to see who
contributed which references and when.

Logged events (high-signal only — canvas-edit noise intentionally skipped):
- image / video / pdf added (whether dropped, pasted, or pulled from a URL)
- board created / renamed / deleted
- thread started, resolved, reopened
- comment posted on a thread

Backend:
- new activity_logs table (id, board_id, user_id, denormalised actor name +
  email, action, target_type/id/label, metadata JSON, created_at) with an
  index on (board_id, created_at DESC).
- logActivity helper resolves the user once at log time and stores their
  display name + email so entries survive deactivation/rename.
- recordActivity wraps logActivity + a Socket.IO emit to the board's room
  so the panel updates live without polling.
- GET /api/boards/:id/activity?limit=&before= for pagination
  (collection-membership gated, viewer+).

Frontend:
- ActivityPanel side-drawer: time-grouped feed (Today / Yesterday / older),
  per-action icons + tone colours (add/remove/edit/comment), pagination
  via "Load older", live append on Socket.IO 'activity:new'.
- Relative timestamps refresh every 30s.
- Wired into Editor + Toolbar.

README updated; roadmap entry checked off.

backend/routes/activity.js

@@ -0,0 +1,35 @@
+const { Router } = require('express');
+const { authMiddleware } = require('../auth');
+const { getBoardActivity } = require('../db');
+const { resolveBoard } = require('./board-access');
+const { formatRow } = require('../activity');
+
+const router = Router();
+router.use(authMiddleware);
+
+/**
+ * GET /api/boards/:boardId/activity
+ * Returns recent activity entries for a board, newest first.
+ *
+ * Query params:
+ *   limit  — max entries to return (1-200, default 50)
+ *   before — ISO timestamp; only entries created strictly before this
+ */
+router.get('/:boardId/activity', (req, res) => {
+  try {
+    const result = resolveBoard(req, res, 'viewer');
+    if (!result) return;
+
+    const { limit, before } = req.query;
+    const rows = getBoardActivity(result.board.id, { limit, before });
+    return res.json({
+      activity: rows.map(formatRow),
+      hasMore: rows.length === Math.max(1, Math.min(parseInt(limit, 10) || 50, 200)),
+    });
+  } catch (err) {
+    console.error('[activity] list error:', err);
+    return res.status(500).json({ error: 'Internal server error' });
+  }
+});
+
+module.exports = router;

backend/routes/boards.js

@@ -12,6 +12,7 @@ const {
   getCollectionMember,
 } = require('../db');
 const { deleteBoardImages: deleteBoardMinioImages } = require('../minio');
+const { recordActivity } = require('../activity');
 
 const router = Router();
 
@@ -81,6 +82,14 @@ router.post('/', (req, res) => {
       createdBy: req.user.id,
     });
 
+    recordActivity(req, {
+      boardId: board.id,
+      action: 'board.created',
+      targetType: 'board',
+      targetId: board.id,
+      targetLabel: board.name,
+    });
+
     return res.status(201).json({ board });
   } catch (err) {
     console.error('[boards] create error:', err);
@@ -171,8 +180,20 @@ router.put('/:boardId', (req, res) => {
     if (!result) return;
 
     const { name, description } = req.body;
+    const prevName = result.board.name;
     const updated = updateBoard(result.board.id, { name, description });
 
+    if (typeof name === 'string' && name.trim() && name.trim() !== prevName) {
+      recordActivity(req, {
+        boardId: updated.id,
+        action: 'board.renamed',
+        targetType: 'board',
+        targetId: updated.id,
+        targetLabel: updated.name,
+        metadata: { from: prevName, to: updated.name },
+      });
+    }
+
     return res.json({ board: updated });
   } catch (err) {
     console.error('[boards] update error:', err);
@@ -195,6 +216,14 @@ router.delete('/:boardId', async (req, res) => {
       console.error('[boards] MinIO cleanup error:', e);
     }
 
+    recordActivity(req, {
+      boardId: result.board.id,
+      action: 'board.deleted',
+      targetType: 'board',
+      targetId: result.board.id,
+      targetLabel: result.board.name,
+    });
+
     deleteBoard(result.board.id);
 
     return res.json({ message: 'Board deleted' });

backend/routes/threads.js

@@ -18,6 +18,7 @@ const {
   getUserById,
 } = require('../db');
 const { hasCollectionRole, resolveBoard } = require('./board-access');
+const { recordActivity } = require('../activity');
 
 function resolveAuthorName(reqUser) {
   if (reqUser.display_name || reqUser.username) {
@@ -108,6 +109,14 @@ router.post('/:boardId/threads', (req, res) => {
       });
     }
 
+    recordActivity(req, {
+      boardId: req.params.boardId,
+      action: 'thread.created',
+      targetType: 'thread',
+      targetId: threadId,
+      targetLabel: content.trim().slice(0, 80),
+    });
+
     return res.status(201).json({ thread, comment });
   } catch (err) {
     console.error('[threads] create error:', err);
@@ -144,6 +153,15 @@ router.patch('/:boardId/threads/:threadId', (req, res) => {
       });
     }
 
+    if (status === 'resolved' || status === 'open') {
+      recordActivity(req, {
+        boardId: req.params.boardId,
+        action: status === 'resolved' ? 'thread.resolved' : 'thread.reopened',
+        targetType: 'thread',
+        targetId: req.params.threadId,
+      });
+    }
+
     return res.json({ thread: updated });
   } catch (err) {
     console.error('[threads] status error:', err);
@@ -221,6 +239,14 @@ router.post('/:boardId/threads/:threadId/comments', (req, res) => {
       });
     }
 
+    recordActivity(req, {
+      boardId: req.params.boardId,
+      action: 'comment.added',
+      targetType: 'thread',
+      targetId: req.params.threadId,
+      targetLabel: content.trim().slice(0, 80),
+    });
+
     return res.status(201).json({ comment });
   } catch (err) {
     console.error('[threads] add comment error:', err);

backend/routes/upload.js

@@ -6,9 +6,10 @@ const https = require('https');
 const http = require('http');
 const { URL } = require('url');
 const { authMiddleware } = require('../auth');
-const { getBoard, getCollectionMember, createImage, createMediaJob, createPdfPage, updateImagePageCount } = require('../db');
+const { getBoard, getCollectionMember, createImage, getImage, createMediaJob, createPdfPage, updateImagePageCount } = require('../db');
 const { putBuffer, getImageUrl, MIME_TO_EXT, MAX_FILE_SIZE } = require('../minio');
 const { pdfInfo, bufferToTempFile } = require('../pdf-utils');
+const { recordActivity } = require('../activity');
 
 const router = Router();
 
@@ -192,6 +193,15 @@ router.post('/boards/:boardId/images', upload.single('image'), async (req, res)
           });
         }
 
+        recordActivity(req, {
+          boardId: board.id,
+          action: 'pdf.added',
+          targetType: 'pdf',
+          targetId: imageId,
+          targetLabel: originalname,
+          metadata: { pageCount: info.pageCount, fileSize: size },
+        });
+
         return res.status(201).json({
           id: image.id,
           media_type: 'pdf',
@@ -233,6 +243,15 @@ router.post('/boards/:boardId/images', upload.single('image'), async (req, res)
       createMediaJob({ id: jobId, imageId, boardId: board.id, type: 'poster' });
     }
 
+    recordActivity(req, {
+      boardId: board.id,
+      action: `${mediaType}.added`,
+      targetType: mediaType,
+      targetId: imageId,
+      targetLabel: originalname,
+      metadata: { fileSize: size, mimeType: mimetype, source: 'upload' },
+    });
+
     return res.status(201).json({
       id: image.id,
       url: publicUrl,
@@ -354,6 +373,15 @@ router.post('/boards/:boardId/images/from-url', async (req, res) => {
       createMediaJob({ id: jobId, imageId, boardId: board.id, type: 'poster' });
     }
 
+    recordActivity(req, {
+      boardId: board.id,
+      action: `${mediaType}.added`,
+      targetType: mediaType,
+      targetId: imageId,
+      targetLabel: filename,
+      metadata: { fileSize: buffer.length, mimeType, source: 'url', sourceUrl: url },
+    });
+
     return res.status(201).json({
       id: image.id,
       url: publicUrl,