Add notification hook, directory CLAUDE.md scaffolding

- Wire Notification event in settings.json to new notify.sh hook
- notify.sh: Windows toast notifications via PowerShell balloon tip
- docs/CLAUDE.md: authoring standards for ADRs, TR registry, control manifest, engine reference
- design/CLAUDE.md: GDD directory guidance placeholder
- src/: scaffold with .gitkeep and CLAUDE.md authoring guide

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

docs/CLAUDE.md

@@ -0,0 +1,33 @@
+# Docs Directory
+
+When authoring or editing files in this directory, follow these standards.
+
+## Architecture Decision Records (`docs/architecture/`)
+
+Use the ADR template: `.claude/docs/templates/adr.md`
+
+**Required sections:** Title, Status, Context, Decision, Consequences,
+ADR Dependencies, Engine Compatibility, GDD Requirements Addressed
+
+**Status lifecycle:** `Proposed` → `Accepted` → `Superseded`
+- Never skip `Accepted` — stories referencing a `Proposed` ADR are auto-blocked
+- Use `/architecture-decision` to create ADRs through the guided flow
+
+**TR Registry:** `docs/architecture/tr-registry.yaml`
+- Stable requirement IDs (e.g. `TR-MOV-001`) that link GDD requirements to stories
+- Never renumber existing IDs — only append new ones
+- Updated by `/architecture-review` Phase 8
+
+**Control Manifest:** `docs/architecture/control-manifest.md`
+- Flat programmer rules sheet: Required / Forbidden / Guardrails per layer
+- Date-stamped `Manifest Version:` in header
+- Stories embed this version; `/story-done` checks for staleness
+
+**Validation:** Run `/architecture-review` after completing a set of ADRs.
+
+## Engine Reference (`docs/engine-reference/`)
+
+Version-pinned engine API snapshots. **Always check here before using any
+engine API** — the LLM's training data predates the pinned engine version.
+
+Current engine: see `docs/engine-reference/godot/VERSION.md`