Add tracks — auto-updating note blocks with scheduled and event-driven triggers

Track blocks are YAML-fenced sections embedded in markdown notes whose output
is rewritten by a background agent. Three trigger types: manual (Run button or
Copilot), scheduled (cron / window / once with a 2 min grace window), and
event-driven (Gmail/Calendar sync events routed via an LLM classifier with a
second-pass agent decision). Output lives between <!--track-target:ID-->
comment markers that render as editable content in the Tiptap editor so users
can read and extend AI-generated content inline.

Core:
- Schedule and event pipelines run as independent polling loops (15s / 5s),
  both calling the same triggerTrackUpdate orchestrator. Events are FIFO via
  monotonic IDs; a per-track Set guards against duplicate runs.
- Track-run agent builds three message variants (manual/timed/event) — the
  event variant includes a Pass 2 directive to skip updates on false positives
  flagged by the liberal Pass 1 router.
- IPC surface: track:run/get/update/replaceYaml/delete plus tracks:events
  forward of the pub-sub bus to the renderer.
- Gmail emits per-thread events; Calendar bundles a digest per sync.

Copilot:
- New `tracks` skill (auto-generated canonical schema from Zod via
  z.toJSONSchema) teaches block creation, editing, and proactive suggestion.
- `run-track-block` tool with optional `context` parameter for backfills
  (e.g. seeding a new email-tracking block from existing synced emails).

Renderer:
- Tiptap chip (display-only) opens a rich modal with tabs, toggle, schedule
  details, raw YAML editor, and confirm-to-delete. All mutations go through
  IPC so the backend stays the single writer.
- Target regions use two atom marker nodes (open/close) around real editable
  content — custom blocks render natively, users can add their own notes.
- "Edit with Copilot" seeds a chat session with the note attached.

Docs: apps/x/TRACKS.md covers product flows, technical pipeline, and a
catalog of every LLM prompt involved with file+line pointers.

apps/x/packages/shared/src/index.ts

@@ -9,6 +9,7 @@ export * as agentScheduleState from './agent-schedule-state.js';
 export * as serviceEvents from './service-events.js'
 export * as inlineTask from './inline-task.js';
 export * as blocks from './blocks.js';
+export * as trackBlock from './track-block.js';
 export * as frontmatter from './frontmatter.js';
 export * as bases from './bases.js';
 export { PrefixLogger };