M6: browse notes by creation date (Timeline lens)

A temporal recall path — find a note by WHEN it was captured, not just what it contains (task 1903, first of the M6 recall items).

Backend: list_notes gains an optional created_at range (created_after / created_before, half-open interval) + sort=created; also lays groundwork for the richer-search facets (task 1902). New _parse_iso_dt helper with a DB-free unit test.

Frontend: a Timeline view (sidebar nav + 'g t' + command palette) grouping active notes newest-first into local-time buckets (Today / Yesterday / Earlier this week / this month / Month YYYY), plus an optional From/To date filter. Built as a lens on the same NoteCard masonry, consistent with the existing Reminders/Search views.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/AppShell.vue

@@ -32,6 +32,7 @@ const shortcuts = [
   { label: "Go to Board", keys: ["g", "b"] },
   { label: "Go to Graph", keys: ["g", "g"] },
   { label: "Go to Reminders", keys: ["g", "r"] },
+  { label: "Go to Timeline", keys: ["g", "t"] },
   { label: "Move card focus", keys: ["j", "k"] },
   { label: "Open focused card", keys: ["Enter"] },
   { label: "Pin / archive / trash card", keys: ["#", "e", "x"] },
@@ -102,6 +103,11 @@ function onKeydown(e: KeyboardEvent) {
       void router.push("/reminders");
       return;
     }
+    if (e.key === "t") {
+      e.preventDefault();
+      void router.push("/timeline");
+      return;
+    }
   }
   if (e.key === "/") {
     e.preventDefault();
@@ -286,6 +292,13 @@ async function signOut() {
           >
             <Icon name="bell" /> Reminders
           </RouterLink>
+          <RouterLink
+            to="/timeline"
+            class="nav-link"
+            :class="route.name === 'timeline' ? 'nav-link-active' : ''"
+          >
+            <Icon name="calendar" /> Timeline
+          </RouterLink>
         </nav>
       </aside>