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>

scripts/update-core.ts

@@ -0,0 +1,36 @@
+#!/usr/bin/env tsx
+import { applyUpdate, previewUpdate } from '../skills-engine/update.js';
+
+const newCorePath = process.argv[2];
+if (!newCorePath) {
+  console.error('Usage: tsx scripts/update-core.ts <path-to-new-core>');
+  process.exit(1);
+}
+
+// Preview
+const preview = previewUpdate(newCorePath);
+console.log('=== Update Preview ===');
+console.log(`Current version: ${preview.currentVersion}`);
+console.log(`New version:     ${preview.newVersion}`);
+console.log(`Files changed:   ${preview.filesChanged.length}`);
+if (preview.filesChanged.length > 0) {
+  for (const f of preview.filesChanged) {
+    console.log(`  ${f}`);
+  }
+}
+if (preview.conflictRisk.length > 0) {
+  console.log(`Conflict risk:   ${preview.conflictRisk.join(', ')}`);
+}
+if (preview.customPatchesAtRisk.length > 0) {
+  console.log(`Custom patches at risk: ${preview.customPatchesAtRisk.join(', ')}`);
+}
+console.log('');
+
+// Apply
+console.log('Applying update...');
+const result = await applyUpdate(newCorePath);
+console.log(JSON.stringify(result, null, 2));
+
+if (!result.success) {
+  process.exit(1);
+}