feat(framework): production SSR build (#88)

[qantrepreneur]

Summary

• Add src/server.ts entry point to playground that wires createRequestHandler with route manifest
• Update playground build script to vite build --ssr src/server.ts
• Make matchRoute and createRequestHandler generic over route types via new MatchableRoute base type
• Add ManifestRouteEntry type for typed manifest route entries with load() function
• Strip .tsx/.ts extensions from generated route manifest imports for TypeScript compatibility
• Runtime type guards (isPageModule, isHandlerModule, isTemplateId) instead of casts in server entry
• Use pickRouteModule to extract page/handler from ESM module (fixes latent runtime bug where raw module was passed instead of the export)
• Use async/await in loadTemplate instead of .then()
• Use tabs in codegen output to match Prettier config
• Allow export default in server.ts via ESLint override

Test plan

• vite build --ssr src/server.ts produces working bundle in dist/
• Built bundle exports a request handler function
• Route transforms correctly inject paths in build output
• All framework tests pass (258 tests)
• Codegen tests updated for tab indentation and extensionless imports
• Type check passes across monorepo
• Lint and Prettier checks pass

Closes #88

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