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/CommandPalette.vue

@@ -43,6 +43,7 @@ const commands = computed<Row[]>(() => {
     { id: "cmd:board", label: "Go to Board", hint: "Navigate", run: () => go("/") },
     { id: "cmd:graph", label: "Go to Graph", hint: "Navigate", run: () => go("/graph") },
     { id: "cmd:reminders", label: "Go to Reminders", hint: "Navigate", run: () => go("/reminders") },
+    { id: "cmd:timeline", label: "Go to Timeline", hint: "Navigate", run: () => go("/timeline") },
     { id: "cmd:archive", label: "Go to Archive", hint: "Navigate", run: () => go("/archive") },
     { id: "cmd:trash", label: "Go to Trash", hint: "Navigate", run: () => go("/trash") },
   ];