feat(mapper): add FastAPI route mapping

[mbelinky]

Summary

• Add FastAPI route feature mapping for Python projects, including root-level app files and web/ source roots.
• Detect Python web/test frameworks from Python dependency metadata.
• Update README, docs, and static site copy for Python and FastAPI mapping coverage.

Why

Python projects can expose their web entrypoints through root-level app files and FastAPI decorators. Mapping those as route-sized features gives review runs better coverage than broad source groups alone.

Validation

• pnpm typecheck
• pnpm test -- src/mapper.test.ts
• pnpm lint
• pnpm build
• Local dry-run against a FastAPI/Python repository confirmed root app files and route-sized FastAPI features are produced

Red-team notes

• FastAPI route mapping requires per-file FastAPI imports before parsing decorator routes.
• Decorator targets are limited to app/router/api-style identifiers to avoid generic client/helper method decorators.
• Known limitation: mounted router prefixes are not expanded into full deployed paths in this first pass.
• Known limitation: non-literal route paths or methods are intentionally skipped/defaulted rather than guessed.