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/router/index.ts

@@ -18,6 +18,7 @@ const router = createRouter({
         { path: "search", name: "search", component: () => import("../views/SearchView.vue") },
         { path: "graph", name: "graph", component: () => import("../views/GraphView.vue") },
         { path: "reminders", name: "reminders", component: () => import("../views/RemindersView.vue") },
+        { path: "timeline", name: "timeline", component: () => import("../views/TimelineView.vue") },
       ],
     },
     {