Rename API contracts to web routes for clarity

Changed terminology from "API" to "Routes" to better reflect server-rendered HTML approach:
- Renamed submission_api.md → submission_routes.md
- Renamed dashboard_api.md → dashboard_routes.md
- Renamed admin_api.md → admin_routes.md
- Updated headers to clarify "Response Type: Server-rendered HTML (no JavaScript required)"
- Updated references in plan.md and quickstart.md

This clarifies that the application uses traditional web routes with form submissions
and HTML responses, not REST API endpoints with JSON.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

specs/001-build-an-application/plan.md

@@ -177,7 +177,7 @@ Data model and API contracts support independent implementation of P1→P2→P3
 Generated artifacts:
 - ✅ research.md (7 decision records)
 - ✅ data-model.md (6 entities fully specified)
-- ✅ contracts/ (3 API contract documents: submission, dashboard, admin)
+- ✅ contracts/ (3 web route contracts: submission, dashboard, admin)
 - ✅ quickstart.md (developer onboarding guide)
 - ✅ CLAUDE.md (agent context updated)