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>

.github/workflows/skill-tests.yml

@@ -0,0 +1,84 @@
+name: Skill Combination Tests
+
+on:
+  pull_request:
+    branches: [main]
+    paths:
+      - 'skills-engine/**'
+      - '.claude/skills/**'
+      - 'src/**'
+
+jobs:
+  generate-matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.matrix.outputs.matrix }}
+      has_entries: ${{ steps.matrix.outputs.has_entries }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - name: Generate overlap matrix
+        id: matrix
+        run: |
+          MATRIX=$(npx tsx scripts/generate-ci-matrix.ts)
+          {
+            echo "matrix<<MATRIX_EOF"
+            echo "$MATRIX"
+            echo "MATRIX_EOF"
+          } >> "$GITHUB_OUTPUT"
+          if [ "$MATRIX" = "[]" ]; then
+            echo "has_entries=false" >> "$GITHUB_OUTPUT"
+          else
+            echo "has_entries=true" >> "$GITHUB_OUTPUT"
+          fi
+
+  test-combinations:
+    needs: generate-matrix
+    if: needs.generate-matrix.outputs.has_entries == 'true'
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        entry: ${{ fromJson(needs.generate-matrix.outputs.matrix) }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+
+      - name: Initialize nanoclaw dir
+        run: npx tsx -e "import { initNanoclawDir } from './skills-engine/index.js'; initNanoclawDir();"
+
+      - name: Apply skills in sequence
+        run: |
+          for skill in $(echo '${{ toJson(matrix.entry.skills) }}' | jq -r '.[]'); do
+            echo "Applying skill: $skill"
+            npx tsx scripts/apply-skill.ts ".claude/skills/$skill"
+          done
+
+      - name: Run skill tests
+        run: npx vitest run --config vitest.skills.config.ts
+
+  skill-tests-summary:
+    needs: [generate-matrix, test-combinations]
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+      - name: Report result
+        run: |
+          if [ "${{ needs.generate-matrix.outputs.has_entries }}" = "false" ]; then
+            echo "No overlapping skills found. Skipped combination tests."
+            exit 0
+          fi
+          if [ "${{ needs.test-combinations.result }}" = "success" ]; then
+            echo "All skill combination tests passed."
+          else
+            echo "Some skill combination tests failed."
+            exit 1
+          fi