feat: session quick wins (#51-#55) (#72)

* feat: add session quick wins (#51-#55)

- Session timer showing elapsed time in header (#51)
- Tab keyboard shortcut to focus notes textarea (#52)
- Repeat Last Session button on tree library page (#53)
- Auto-recovery banner for incomplete sessions (#54)
- Copy individual step to clipboard on session detail (#55)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: add missing delete button to table and list tree views

The onDeleteTree prop was accepted but never used in TreeTableView and
TreeListView. Now both views show a trash icon (permission-gated) matching
the existing grid view behavior.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/hooks/useKeyboardShortcuts.ts

@@ -82,6 +82,13 @@ export function useTreeNavigationShortcuts({
       handler: onContinue,
       enabled: canContinue,
     },
+    // Tab to focus notes
+    {
+      key: 'Tab',
+      handler: () => {
+        document.getElementById('session-notes')?.focus()
+      },
+    },
   ]
 
   useKeyboardShortcuts(shortcuts)