fix: remove tiktoken dependency to resolve WASM runtime error in serverless

**Problem:**
The Interactive Playground was failing with "Missing tiktoken_bg.wasm" error in production. Tiktoken requires WASM files which don't work in Vercel's serverless environment.

**Solution:**
- Remove tiktoken import from tool-executor-agent
- Replace tiktoken-based token counting with character estimation (~4 chars/token)
- Remove tiktoken from package.json dependencies
- Remove unused biome-ignore comment

**Impact:**
- Token counting is now approximate but consistent
- No more WASM-related runtime errors
- Serverless deployment works properly
- Tool execution now functional in production

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

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

apps/web/src/lib/ai-agent/tool-executor-agent.ts

@@ -183,7 +183,6 @@ export async function executeToolWithAgent(
     model: openai('gpt-4-turbo'),
     messages,
     tools: {
-      // biome-ignore lint/suspicious/noExplicitAny: AI SDK v5 streaming type compatibility
       [tool.npmPackageName]: toolDef,
     },
     // biome-ignore lint/suspicious/noExplicitAny: AI SDK v5 chunk type compatibility