ci: add npm publish workflow

Adds .github/workflows/publish.yml - triggers on git tag v*.
Runs npm publish --access public using NPM_TOKEN secret.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: homeofe

.ai/handoff/MANIFEST.json

@@ -8,11 +8,11 @@
   "quick_context": "commitprompt v0.1.0 published on npm. 59/59 tests passing. GitHub Actions and GitLab CI live. ESLint with typescript-eslint and custom no-em-dash rule configured. All tasks done.",
   "last_session": {
     "agent": "claude-code",
-    "duration_minutes": 5,
+    "duration_minutes": 2,
     "session_id": "eslint-setup",
     "phase": "maintenance",
     "commit": "54bbf76",
-    "timestamp": "2026-02-27T14:00:00.000Z"
+    "timestamp": "2026-02-27T14:12:58.298Z"
   },
   "tasks": {
     "T-003": {
@@ -37,7 +37,7 @@
       "created": "2026-02-28T00:00:00Z",
       "depends_on": [],
       "priority": "low",
-      "completed": "2026-02-27T14:00:00.000Z"
+      "completed": "2026-02-27T14:12:58.299Z"
     }
   },
   "next_task_id": 4,

.github/workflows/publish.yml

@@ -0,0 +1,22 @@
+name: Publish to npm
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          registry-url: 'https://registry.npmjs.org'
+      - run: npm ci
+      - run: npm publish --access public
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}