[Flask] Add route resolver

[theDakshJaitly]

Target branch: main

Dependency

The Python code-graph extractor was merged in #103 and is available on main.
This issue is not blocked by another language extractor.

Goal

Add a bounded Flask framework resolver that connects decorator-defined routes
to their handler functions.

The initial implementation should cover conventional Flask application and
Blueprint decorators whose methods and paths can be determined statically.

Scope

• Detect Flask from declared project dependencies such as pyproject.toml
  or requirements files.
• Recognize:
  • @app.route("/path")
  • @app.route("/path", methods=["GET", "POST"])
  • Shortcut decorators such as @app.get() and @app.post()
  • Equivalent decorators on Blueprint instances
• Treat @app.route() without an explicit methods list as a GET route.
• Emit a separate stable route node for each explicitly declared HTTP method.
• Emit a function_ref from each route node to the decorated handler.
• Resolve the reference only when the matching same-file function or method is
  unambiguous.
• Preserve Flask path converters such as /users/<int:user_id>.
• Leave missing or ambiguous handlers unresolved rather than guessing.

Required changes

• Add src/graph/resolution/frameworks/flask.ts implementing
  FrameworkResolver.
• Register and export it from
  src/graph/resolution/frameworks/index.ts.
• Add a minimal Flask fixture under
  src/graph/__tests__/fixtures/.
• Add focused detection, extraction, resolution, and ambiguity tests.

Acceptance criteria

• Positive and negative Flask detection are tested.
• Application and Blueprint route decorators are covered.
• Default GET, explicit method lists, and shortcut decorators are tested.
• Parameterized paths using Flask converters are preserved.
• Both synchronous and asynchronous handlers are covered.
• Route nodes use stable IDs and Python as their language.
• Same-file handlers resolve only when unambiguous.
• Missing and ambiguous handlers remain unresolved.
• The resolver is registered in the framework registry.
• npm run typecheck, npm test, and npm run build pass.
• No identity, reconciliation, schema, or drift-semantics changes are included.

Out of scope

• Composing Blueprint prefixes across register_blueprint() calls.
• add_url_rule() and dynamically registered routes.
• MethodView, Flask extensions, middleware, and application factories.
• Flask's implicit HEAD and OPTIONS behavior.
• Dynamic or computed route paths.
• Evaluating or importing the Flask application.

Contributor references

• Extending the code graph
• src/graph/resolution/frameworks/express.ts
• src/graph/__tests__/resolver-express.test.ts

Contributor workflow

git switch main
git pull
git switch -c feat/flask-route-resolver

Open the pull request with main as the base branch.