fix(attachments): address review findings on attachment history drawer (#121)

Follow-up fixes applied during review of PR #121 (all confirmed minor/nit;
no blockers). Security posture verified sound (externalPath never leaves
toState()/the list route; re-registration runs the guard).

- fix(recovery): restoreAttachmentHistory now skips malformed/legacy saved
  items (null, non-object, missing source/fileName) instead of throwing inside
  the Session constructor — a corrupt __attachmentHistory entry could otherwise
  abort the entire mux-recovery loop. (P1)
- fix(routes): the attachment-list route degrades a single failing entry to
  {missing:true} instead of failing the whole drawer. (INT-4)
- fix(ui): give the attachments header button a positioning context so the
  unread badge anchors to the icon, not the header bar. (F1/CSS-1)
- fix(ui): cancel the debounced history refresh on drawer close and guard it
  against a stale session/closed drawer. (F3)
- fix(ui): re-show ("Card") of a detected item now uses the item's own
  timestamp so the cardId is stable — focuses the existing card instead of
  stacking duplicates. (F4)
- fix(ui): Escape now closes the drawer, matching every other panel. (UX-1)
- fix(ui): badge shows "99+" past 99 (was an inconsistent 100/99 cap). (BADGE-1)
- style: drop the duplicate @keyframes notif-badge-pulse (dead CSS). (INT-1/CSS-3)
- style: empty-state used three undefined CSS custom properties
  (--text-primary/--border-color/--bg-tertiary) → use the defined
  --text/--border-light/--bg-input tokens. (CSS-2)
- test: add constructor restore round-trip + malformed-item resilience tests.

Deferred (noted for author): broadcasting the full 100-item history in every
session-state SSE event (payload bloat), "unread" badge semantics, making the
header button opt-in, and app.inject route tests for the two new endpoints.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/public/panels-ui.js

@@ -2561,7 +2561,17 @@ Object.assign(CodemanApp.prototype, {
       if (data.sessionId === this.activeSessionId) {
         this.updateAttachmentHistoryBadge();
         if (this.attachmentHistoryDrawerOpen) {
-          this._debouncedCall('attachmentHistoryRefresh', () => this.loadAttachmentHistory(data.sessionId), 250);
+          this._debouncedCall(
+            'attachmentHistoryRefresh',
+            () => {
+              // The drawer may have closed or the active session changed during
+              // the debounce window — don't refresh for a stale session.
+              if (this.attachmentHistoryDrawerOpen && this.activeSessionId === data.sessionId) {
+                this.loadAttachmentHistory(data.sessionId);
+              }
+            },
+            250
+          );
         }
       }
     }
@@ -2744,7 +2754,7 @@ Object.assign(CodemanApp.prototype, {
     const sessionId = this.activeSessionId;
     const nextCount = count ?? (sessionId ? this.attachmentHistoryCounts.get(sessionId) || 0 : 0);
     if (badge) {
-      badge.textContent = String(Math.min(nextCount, 99));
+      badge.textContent = nextCount > 99 ? '99+' : String(nextCount);
       badge.style.display = nextCount > 0 ? '' : 'none';
     }
     if (button) {
@@ -2804,6 +2814,11 @@ Object.assign(CodemanApp.prototype, {
     const drawer = document.getElementById('attachmentHistoryDrawer');
     this.attachmentHistoryDrawerOpen = false;
     drawer?.classList.remove('open');
+    // Cancel any pending debounced refresh so it can't fire against a closed drawer.
+    if (this._debounceTimers?.attachmentHistoryRefresh) {
+      clearTimeout(this._debounceTimers.attachmentHistoryRefresh);
+      this._debounceTimers.attachmentHistoryRefresh = null;
+    }
     this.updateAttachmentHistoryBadge();
   },
 
@@ -2949,7 +2964,10 @@ Object.assign(CodemanApp.prototype, {
       sessionId: item.sessionId,
       relativePath: item.relativePath,
       fileName: item.fileName,
-      timestamp: Date.now(),
+      // Use the item's own timestamp (not Date.now()) so the derived cardId is
+      // stable across clicks — re-showing focuses the existing card instead of
+      // stacking a duplicate.
+      timestamp: item.timestamp ?? Date.now(),
       size: item.size,
       attachmentType: item.attachmentType,
       extension: item.extension,