docs: nested CLAUDE.md via init-deep

Slim root CLAUDE.md (90 lines) and add 7 nested CLAUDE.md
files for progressive disclosure. Each nested file loads
automatically when Claude reads files in that directory.

Nested files:
- game/        scenarios + NPC phrases (source-of-truth)
- tools/       Python tooling (Runtime 3, TTS, MCP, dev CLI)
- tests/       Python unittest patterns
- specs/       contracts governance
- frontend-scratch-v2/  React 19 + Blockly + Vite (legacy)
- frontend-v3/ pnpm monorepo (production target)
- desktop/     Electron Zacus Studio (macOS)

Root CLAUDE.md gains a Where-to-Look table and pointer to
nested guidance. ESP32_ZACUS submodule is intentionally not
covered (separate repo with its own CI).

specs/CLAUDE.md

@@ -0,0 +1,31 @@
+# Specs
+
+Contracts between firmware, frontends, tooling, and AI agents. Treat each spec as a versioned interface — a breaking change here triggers work in 2+ subsystems.
+
+## Canonical Specs
+
+| Spec | Governs |
+|------|---------|
+| `ZACUS_RUNTIME_3_SPEC.md` | Scenario IR + execution semantics |
+| `AI_INTEGRATION_SPEC.md` | Agent layer (hints, voice, vision, TTS, audio_gen, MCP) |
+| `FIRMWARE_WEB_DATA_CONTRACT.md` | ESP32 ↔ frontend HTTP/WebSocket payloads |
+| `MCP_HARDWARE_SERVER_SPEC.md` | MCP stdio tools (6) for hardware interaction |
+| `MEDIA_MANAGER_*` | Media manager (firmware/frontend/runtime/sync) |
+| `STORY_DESIGNER_SCRATCH_LIKE_SPEC.md` | Frontend Blockly-like authoring |
+| `STORY_RUNTIME_API_JSON_CONTRACT.md` | Runtime API JSON shape |
+| `LOCAL_AI_STUDIO_SPEC.md` | Local AI studio integration |
+| `QA_TEST_MATRIX_SPEC.md` | QA matrix + acceptance criteria |
+
+## Editing Rules
+
+- A spec change is a contract change. List affected consumers in the PR description.
+- Bump the version header at the top of the file when altering existing fields; never silently rename keys.
+- New spec docs must be linked from root `CLAUDE.md` "Canonical Files" if they introduce a new contract.
+- Pair runtime/frontend spec changes — the matching `tools/scenario/compile_runtime3.py` and `frontend-scratch-v2/src/lib/runtime3.ts` updates ship in the same PR.
+
+## Anti-Patterns
+
+- "Implementation detail" comments in specs — if it's not part of the contract, remove it
+- Adding fields without specifying optionality, defaults, and version
+- Letting the IR drift between Python compiler and TS runtime without updating the spec first
+- Documenting hardware pins/ports here — they belong in `ESP32_ZACUS/` firmware sources