[Task]: Make Flask a thin web adapter around navigation #79

Motivation

routes.py currently handles graph loading, error interpretation, identity parsing, floor bounds, and response shape. Flask should translate web inputs into a navigation request and navigation results into a page model, rather than carry domain/data knowledge.

Proposed change

Construct navigation in create_app() and retain it in app.extensions or the established application context. Routes should get building/location options through the navigation interface, turn submitted fields into validated route requests, map domain results/errors to explicit page-model fields, preserve selections on error, and pass explicit floor segments to templates. Remove hard-coded development endpoints such as /api/test unless they are justified.

Affected modules or data

• app/__init__.py, app/routes.py, templates/page models, and route tests
• The navigation interface created by the deep-navigation module
• No CSS redesign, database migration, or new public API version

Acceptance criteria

• create_app() owns navigation construction.
• Routes depend only on the navigation interface, not JSON/NetworkX or node-ID parsing.
• Domain failures produce intentional user-facing responses.
• Multi-floor results reach the page as explicit segments.
• Tests inject controlled navigation behavior.
• Route tests cover missing fields, invalid IDs, same-node, no-route, preference-only failure, success, and multi-floor page models.
• Hard-coded test endpoints are removed or justified and just check passes.

Testing requirements

Use controlled navigation implementations in Flask/route tests instead of filesystem/global-graph setup. Exercise rendered page models and error preservation.

Dependencies and risks

This depends on the deep-navigation module. Keep it separate from navigation-domain design so both seams can be reviewed independently.