fix: OS release prep - bootstrap script, deps, docs

- Fix bootstrap script (.env.example.local → .env.example)
- Fix @langchain/core version conflict (^1.0.1 → ^0.3.0)
- Add settings:open event listener for LocalKeyGate button
- Pin Next.js to 15.1.3 (was "latest")
- Default runtime to 'local' mode
- Remove desktop app references from UI text
- Rewrite MCP docs for web-only context
- Add SECURITY.md, CODE_OF_CONDUCT.md, CHANGELOG.md
- Add docs/README.md, docs/TROUBLESHOOTING.md
- Update README with platform support table

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -24,7 +24,7 @@
     "@ai-sdk/anthropic": "^2.0.27",
     "@ai-sdk/openai": "^2.0.22",
     "@ai-sdk/react": "^2.0.26",
-    "@langchain/core": "^1.0.1",
+    "@langchain/core": "^0.3.0",
     "@langchain/textsplitters": "^0.1.0",
     "@radix-ui/react-checkbox": "^1.1.1",
     "@radix-ui/react-dropdown-menu": "^2.1.1",
@@ -36,7 +36,7 @@
     "class-variance-authority": "^0.7.0",
     "clsx": "^2.1.1",
     "lucide-react": "^0.468.0",
-    "next": "latest",
+    "next": "15.1.3",
     "next-themes": "^0.4.3",
     "openai": "^4.103.0",
     "pdf-parse": "^1.1.1",
@@ -60,7 +60,7 @@
     "autoprefixer": "^10.4.20",
     "esbuild": "^0.23.1",
     "eslint": "^8.57.0",
-    "eslint-config-next": "latest",
+    "eslint-config-next": "15.1.3",
     "postcss": "^8.4.49",
     "prettier": "^3.3.3",
     "tailwindcss": "^3.4.17",