feat: add dynamic tool loading system with Railway executor

Implements a complete dynamic tool loading system that allows the playground to discover and load tools from the TPMJS registry at runtime.

**Architecture:**
- Search tool package (@tpmjs/search-registry) - Searches registry for tools
- Search API endpoint (/api/tools/search) - Text-based search with scoring
- Pre-flight tool loading - Automatically searches and loads tools on every message
- Railway executor service (Deno) - Loads tools from esm.sh via HTTP imports
- Dynamic tool loader - Calls Railway to load and execute tools remotely

**Key Components:**

1. Railway Executor (apps/railway-executor/)
   - Deno-based service that natively supports HTTP imports
   - Endpoints: /load-and-describe, /execute-tool, /cache/stats, /cache/clear
   - Deploys to Railway with deno run --allow-net --allow-env server.ts

2. Search Tool Package (packages/tools/search-registry/)
   - AI SDK v6 tool for searching TPMJS registry
   - Uses jsonSchema + inputSchema pattern
   - Searches /api/tools/search endpoint

3. Search API (apps/web/src/app/api/tools/search/)
   - Text-based search with composite scoring
   - Scores: text relevance + quality boost + download boost
   - Returns tool metadata with importUrl for dynamic loading

4. Dynamic Tool Loader (apps/playground/src/lib/dynamic-tool-loader.ts)
   - Calls Railway service to load tools from esm.sh
   - Creates tool wrappers that execute remotely
   - Process-level module cache + per-conversation tracking

5. Pre-flight Loading (apps/playground/src/app/api/chat/route.ts)
   - Automatically searches for tools on every user message
   - Loads top 5 matching tools before agent processes request
   - Merges with static tools for seamless experience

**Technical Decisions:**
- Deno over Node.js: Native HTTP import support without flags
- Remote execution: Tools run in Railway sandbox, not Vercel
- Pre-flight loading: Better UX than two-turn search pattern
- Text search: BM25 had dependency issues, simple scoring works well

**Environment Variables:**
- RAILWAY_SERVICE_URL: https://endearing-commitment-production.up.railway.app

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

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

apps/web/package.json

@@ -21,6 +21,7 @@
     "@tpmjs/utils": "workspace:*",
     "@types/react-syntax-highlighter": "^15.5.13",
     "ai": "6.0.0-beta.124",
+    "bm25": "^0.1.1",
     "next": "^16.0.4",
     "next-themes": "^0.4.6",
     "openai": "^6.9.1",