Project Workspace view, abort button, session invalidation, workspace fixes

Workspace (/workspace/:projectId):
- Three-panel layout (tasks / chat / notes) with CSS grid collapse toggles
- WorkspaceTaskPanel: tasks grouped by milestone, collapsible groups, task
  detail slide-over with status cycling, TaskLogSection work log, and
  inline-confirm delete
- WorkspaceNoteEditor: list view (sorted by updated_at, inline tag pills,
  inline-confirm delete) with editor view (TipTap, TagInput, Suggest tags,
  60s autosave)
- Persistent workspace conversation stored in localStorage per project;
  reused on return visits
- Thinking enabled (think: true) with Reasoning block in streaming bubble
- workspace_project_id backend pipeline: chat.py → generation_task.py →
  llm.py; system prompt uses project title so agent passes project="Title"
  to tools (fixes create_note failing with numeric project string)
- SSE tool-call watcher bridges agent actions to panel updates
- Height fix: workspace-root uses height 100%; app-content switches to
  overflow hidden via :has() selector
- Entry point: "Open Workspace" button on ProjectView

Abort button:
- Stop button in ChatView header and WorkspaceView input bar
- Calls existing cancelGeneration() / POST .../generation/cancel

Session invalidation:
- POST /api/auth/invalidate-sessions bumps session_version, keeps current
  session alive; useful after SSO/OAuth password rotation
- Button in Settings → Active Sessions section

Other:
- Dashboard recent notes limit increased from 8 to 16
- Workspace chat abort replaces Send button while streaming

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

frontend/src/views/ChatView.vue

@@ -458,6 +458,14 @@ onUnmounted(() => {
             </svg>
           </button>
           <h2>{{ store.currentConversation.title || "New Chat" }}</h2>
+          <button
+            v-if="store.streaming"
+            class="btn-abort"
+            @click="store.cancelGeneration()"
+            title="Stop generation"
+          >
+            ■ Stop
+          </button>
           <button
             v-if="store.currentConversation.messages.length"
             class="btn-summarize"
@@ -834,6 +842,22 @@ onUnmounted(() => {
   min-width: 0;
 }
 
+.btn-abort {
+  padding: 0.3rem 0.75rem;
+  background: none;
+  color: var(--color-danger, #e74c3c);
+  border: 1px solid var(--color-danger, #e74c3c);
+  border-radius: var(--radius-sm);
+  cursor: pointer;
+  font-size: 0.85rem;
+  white-space: nowrap;
+  font-weight: 600;
+}
+.btn-abort:hover {
+  background: var(--color-danger, #e74c3c);
+  color: #fff;
+}
+
 .btn-summarize {
   padding: 0.3rem 0.75rem;
   background: var(--color-bg-secondary);