feat: add interactive tool playground with AI-powered execution

Implement comprehensive tool testing environment with real package execution, AI agents, and token tracking.

**New Features:**
- Interactive playground UI with 4 tabs (Input, Output, Logs, Token Usage)
- Real npm package execution in VM2 sandbox with security constraints
- AI-powered tool execution using AI SDK v5 and GPT-4 Turbo
- Server-Sent Events (SSE) streaming for real-time progress updates
- Comprehensive 4-category token tracking (Input, Tool Description, Schema, Output)
- Visual token breakdown with colored progress bars
- IP-based rate limiting (10 executions/hour per IP)
- Database persistence of all simulations with full metadata

**Database Schema:**
- New `Simulation` model for execution records
- New `TokenUsage` model for detailed token metrics
- New `ExecutionLog` model for execution event tracking
- Added simulations relation to Tool model

**Package Executor (@tpmjs/package-executor):**
- VM2 sandbox with 5-second timeout
- Blocked dangerous modules (fs, net, http, https, child_process)
- LRU file system cache in /tmp/.tpmjs-cache
- Package installation and caching strategy

**AI Agent Service:**
- TPMJS parameter to Zod schema conversion
- AI SDK tool definition generation
- Token counting using tiktoken library
- GPT-4 Turbo pricing estimation
- Streaming text execution with callbacks

**API Endpoints:**
- POST /api/tools/[...slug]/execute - SSE streaming execution
- GET /api/tools/[...slug]/simulations - Execution history
- Rate limit headers (X-RateLimit-Limit, X-RateLimit-Remaining)

**Frontend Components:**
- ToolPlayground - Main playground UI with tabs
- TokenBreakdown - Visual token metrics with colored bars
- Integrated above README section on tool detail pages

**Security:**
- VM2 sandboxing prevents filesystem/network access
- Rate limiting prevents abuse
- IP tracking for usage monitoring
- Timeout protection (60s max API duration, 5s VM timeout)

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

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

apps/web/package.json

@@ -11,15 +11,19 @@
     "clean": "rm -rf .next .turbo"
   },
   "dependencies": {
+    "@ai-sdk/openai": "^2.0.74",
     "@tpmjs/db": "workspace:*",
     "@tpmjs/env": "workspace:*",
     "@tpmjs/npm-client": "workspace:*",
+    "@tpmjs/package-executor": "workspace:*",
     "@tpmjs/types": "workspace:*",
     "@tpmjs/ui": "workspace:*",
     "@tpmjs/utils": "workspace:*",
     "@types/react-syntax-highlighter": "^15.5.13",
+    "ai": "^5.0.104",
     "next": "^16.0.4",
     "next-themes": "^0.4.6",
+    "openai": "^6.9.1",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
     "react-markdown": "^10.1.0",
@@ -27,7 +31,8 @@
     "rehype-raw": "^7.0.0",
     "rehype-sanitize": "^6.0.0",
     "remark-gfm": "^4.0.1",
-    "zod": "^3.24.1"
+    "tiktoken": "^1.0.22",
+    "zod": "^3.25.76"
   },
   "devDependencies": {
     "@tpmjs/eslint-config": "workspace:*",