feat(web): add route manifest for coverage tracking

Document all 46 route patterns across 12 entity types + utility routes.
Enables E2E test coverage tracking and gap analysis.

- Utility routes: 7 (homepage, explore, settings, cache, text, evaluation, autocomplete)
- Special routes: 6 (external ID resolution, OpenAlex URLs, API proxy)
- Entity routes: 33 (12 entity types with index/detail + canonical ID routes)

Related to T015 in specs/020-e2e-test-coverage

Author: Mearman