feat(graph): add Flask route resolver

[abhinav-phi]

Resolves #112.

What

A bounded Flask framework resolver following the express.ts reference pattern. It recognizes:

• @app.route("/path") — GET by default, and methods=["GET", "POST"] fanned out to one stable route node per explicitly declared method
• shortcut decorators @app.get(), @app.post(), @app.put(), @app.patch(), @app.delete(), @app.options(), @app.head()
• the same decorators on Blueprint instances (prefix composition across register_blueprint() stays out of scope, per the issue)

Flask path converters such as /users/<int:user_id> are preserved verbatim — they are the route's identity, and normalizing them would collide distinct routes. Sync and async def handlers both bind; stacked decorators, and blank/comment lines between decorator and def (legal in Python), are handled. Same-file handlers resolve only when unambiguous; missing, cross-file, and duplicate handlers stay unresolved.

One deliberate deviation from the issue text

The issue says to detect Flask from pyproject.toml or requirements files. Those manifests are not staged corpus files — the detection context's getAllFiles()/readFile() only see staged sources plus package/tsconfig config globs — so a manifest-based detect() would return false on every real build while still passing fake-context unit tests. Detection here instead keys on a staged Python module actually importing flask (import flask, from flask import ..., from flask.views import ...), which the context genuinely observes and which every Flask project has. flask_restful and friends do not match. This is verified end-to-end by the integration test, which builds a real graph over a Flask fixture and asserts the persisted route nodes and framework-resolved edges.

Worth flagging for review: the open FastAPI resolver PR (#113) uses the manifest-based detect() and would have the same blind spot in real builds.

Tests

• resolver-flask.test.ts (9): positive/negative detection (including flask_restful), route fan-out with converters preserved, custom instance names with dynamic paths and foreign receivers skipped, resolution of functions and methods, missing/cross-file/ambiguous left unresolved, non-Python files ignored, registry registration.
• resolver-flask-integration.test.ts (1): real rebuildGraph over a Flask fixture — route nodes persist with stable flask-route identity and both methods resolve to the handler through framework edges.

npm run typecheck, npm run build pass; targeted suites green. The three failures in test/graph-integration.test.ts on my Windows machine reproduce identically on clean main (symlink/WAL environment noise) and are unrelated.

No identity, reconciliation, schema, or drift-semantics changes are included.