Extract TypeScript compiler to companion @secure-exec/typescript package

[NathanFlurry]

Summary

Extracts TypeScript compilation and type-checking from the core secure-exec runtime into a new companion package @secure-exec/typescript. The core runtime now executes JavaScript only, with compiler work sandboxed in a dedicated isolate to prevent untrusted type graphs from consuming host resources.

• New createTypeScriptTools() factory with typecheckProject, compileProject, typecheckSource, compileSource methods
• Core runtime cleanup: fixes variable consistency in browser worker transforms and adds regression tests for TypeScript-only syntax failures
• Comprehensive documentation and OpenSpec updates reflecting the JavaScript-only core contract
• Restored typescript devDependency to secure-exec package.json for its own build scripts

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commit: 6306654