feat: add voice transcription as nanorepo skill (#326)

Add voice transcription skill package at
.claude/skills/add-voice-transcription/ so it can be applied via the
skills engine. Skill adds src/transcription.ts (OpenAI Whisper), modifies
whatsapp.ts to detect/transcribe voice notes, and includes intent files,
3 test cases, and 8 skill validation tests.

Also fixes skills engine runNpmInstall() to use --legacy-peer-deps,
needed for any skill adding deps with Zod v3 peer requirements.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/add-voice-transcription/manifest.yaml

@@ -0,0 +1,17 @@
+skill: voice-transcription
+version: 1.0.0
+description: "Voice message transcription via OpenAI Whisper"
+core_version: 0.1.0
+adds:
+  - src/transcription.ts
+modifies:
+  - src/channels/whatsapp.ts
+  - src/channels/whatsapp.test.ts
+structured:
+  npm_dependencies:
+    openai: "^4.77.0"
+  env_additions:
+    - OPENAI_API_KEY
+conflicts: []
+depends: []
+test: "npx vitest run src/channels/whatsapp.test.ts"