Add JS linting and deploy gating to CI pipeline

- Add js-lint job (ESLint 8) for static/ directory
- Add deploy job gated on both python-lint and js-lint passing
- Deploy triggers gandalf-deploy webhook on main branch only
- Add static/.eslintrc.json with browser env config
- Add node_modules/ to .gitignore

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

static/.eslintrc.json

@@ -0,0 +1,13 @@
+{
+    "env": { "browser": true, "es2021": true },
+    "extends": "eslint:recommended",
+    "parserOptions": { "ecmaVersion": 2021, "sourceType": "script" },
+    "rules": {
+        "no-unused-vars": "warn",
+        "no-undef": "off",
+        "no-empty": "warn",
+        "no-inner-declarations": "warn",
+        "semi": ["error", "always"],
+        "eqeqeq": "warn"
+    }
+}