Skills engine v0.1 + multi-channel infrastructure (#307)

* refactor: multi-channel infrastructure with explicit channel/is_group tracking

- Add channels[] array and findChannel() routing in index.ts, replacing
  hardcoded whatsapp.* calls with channel-agnostic callbacks
- Add channel TEXT and is_group INTEGER columns to chats table with
  COALESCE upsert to protect existing values from null overwrites
- is_group defaults to 0 (safe: unknown chats excluded from groups)
- WhatsApp passes explicit channel='whatsapp' and isGroup to onChatMetadata
- getAvailableGroups filters on is_group instead of JID pattern matching
- findChannel logs warnings instead of silently dropping unroutable JIDs
- Migration backfills channel/is_group from JID patterns for existing DBs

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

* feat: skills engine v0.1 — deterministic skill packages with rerere resolution

Three-way merge engine for applying skill packages on top of a core
codebase. Skills declare which files they add/modify, and the engine
uses git merge-file for conflict detection with git rerere for
automatic resolution of previously-seen conflicts.

Key components:
- apply: three-way merge with backup/rollback safety net
- replay: clean-slate replay for uninstall and rebase
- update: core version updates with deletion detection
- rebase: bake applied skills into base (one-way)
- manifest: validation with path traversal protection
- resolution-cache: pre-computed rerere resolutions
- structured: npm deps, env vars, docker-compose merging
- CI: per-skill test matrix with conflict detection

151 unit tests covering merge, rerere, backup, replay, uninstall,
update, rebase, structured ops, and edge cases.

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

* feat: add Discord and Telegram skill packages

Skill packages for adding Discord and Telegram channels to NanoClaw.
Each package includes:
- Channel implementation (add/src/channels/)
- Three-way merge targets for index.ts, config.ts, routing.test.ts
- Intent docs explaining merge invariants
- Standalone integration tests
- manifest.yaml with dependency/conflict declarations

Applied via: npx tsx scripts/apply-skill.ts .claude/skills/add-discord
These are inert until applied — no runtime impact.

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

* remove unused docs (skills-system-status, implementation-guide)

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

---------

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

.claude/skills/add-discord/modify/src/index.ts.intent.md

@@ -0,0 +1,43 @@
+# Intent: src/index.ts modifications
+
+## What changed
+Added Discord as a channel option alongside WhatsApp, introducing multi-channel infrastructure.
+
+## Key sections
+
+### Imports (top of file)
+- Added: `DiscordChannel` from `./channels/discord.js`
+- Added: `DISCORD_BOT_TOKEN`, `DISCORD_ONLY` from `./config.js`
+- Added: `findChannel` from `./router.js`
+- Added: `Channel` from `./types.js`
+
+### Multi-channel infrastructure
+- Added: `const channels: Channel[] = []` array to hold all active channels
+- Changed: `processGroupMessages` uses `findChannel(channels, chatJid)` instead of `whatsapp` directly
+- Changed: `startMessageLoop` uses `findChannel(channels, chatJid)` instead of `whatsapp` directly
+- Changed: `channel.setTyping?.()` instead of `whatsapp.setTyping()`
+- Changed: `channel.sendMessage()` instead of `whatsapp.sendMessage()`
+
+### getAvailableGroups()
+- Unchanged: uses `c.is_group` filter from base (Discord channels pass `isGroup=true` via `onChatMetadata`)
+
+### main()
+- Added: `channelOpts` shared callback object for all channels
+- Changed: WhatsApp conditional to `if (!DISCORD_ONLY)`
+- Added: conditional Discord creation (`if (DISCORD_BOT_TOKEN)`)
+- Changed: shutdown iterates `channels` array instead of just `whatsapp`
+- Changed: subsystems use `findChannel(channels, jid)` for message routing
+
+## Invariants
+- All existing message processing logic (triggers, cursors, idle timers) is preserved
+- The `runAgent` function is completely unchanged
+- State management (loadState/saveState) is unchanged
+- Recovery logic is unchanged
+- Apple Container check is unchanged (ensureContainerSystemRunning)
+
+## Must-keep
+- The `escapeXml` and `formatMessages` re-exports
+- The `_setRegisteredGroups` test helper
+- The `isDirectRun` guard at bottom
+- All error handling and cursor rollback logic in processGroupMessages
+- The outgoing queue flush and reconnection logic (in WhatsAppChannel, not here)