Add automated test coverage for converters

[samsonajulor]

Context

We now have two converter plugins (Express, Flask) with zero automated tests. Both pass CI because there are no *_test.go files — go test ./... has nothing to run.

The Flask converter was merged in #1 based on manual testing. We need proper test coverage before adding more converters.

What's needed

internal/convert/convert_test.go (shared)

• Test routeToHandlerName() with edge cases (nested paths, params, hyphens)
• Test contains() helper
• Test generateFromScan() produces valid Go that compiles

internal/convert/express_test.go

• Create a temp directory with a minimal Express app (app.js, package.json, .env.example)
• Run scanExpress() and assert: route count, methods, DB type, env vars, models
• Verify generated output compiles: go build -o /dev/null .

internal/convert/flask_test.go

• Create a temp directory with a minimal Flask app (app.py, requirements.txt, .env.example)
• Run scanFlask() and assert: route count, methods, DB type, env vars, models
• Test flaskPathToStandard(): <int:id> → :id, <string:name> → :name, <id> → :id
• Test extractMethods(): empty → ["GET"], 'GET', 'POST' → ["GET", "POST"]
• Verify generated output compiles

Test fixtures

• internal/convert/testdata/express/ — minimal Express app
• internal/convert/testdata/flask/ — minimal Flask app

CI

• go test ./... already runs in CI — just needs test files to exist
• Add -race flag for race condition detection
• Add -coverprofile for coverage reporting

Acceptance criteria

• Every converter has at least one end-to-end test (scan → generate → compile)
• Helper functions have unit tests
• go test ./... actually tests something
• CI reports coverage percentage