Fix manga removal and library deletion regressions

[JeremiahM37]

Local manga imports had no removal action or API route. This adds confirmed removal in Library → Manga and DELETE /api/library/manga/{id}, preserving the file on disk and unlinking wanted entries and tags atomically.

Also fixes library removal failures exposed by the regression tests: deleting the last item on a page now returns to an existing page, delayed responses cannot overwrite the current category, and pending removals disable repeat clicks. Audiobookshelf errors are returned instead of reporting a successful deletion. Typed routes reject IDs from other media categories. Kavita series remain managed in Kavita; an explicit source=local selects a local manga ID when Kavita is configured, preventing provider/local ID collisions.

Regression coverage includes all three library categories on desktop/mobile, cancellation, failed deletion and retry, filtered/last-page results, persistence after reload, a real CBZ import/removal journey, authentication, provider failures, and database rollback. Every browser test now fails on uncaught JavaScript errors. New tests run in the existing CI suite.

Validation:

• Full project verify: PASS: 3/3 steps passed, including the React build, Go tests/build, and 64 browser tests (12 new journeys).
• go test -race ./... -count=1.
• go test -tags=integration -race ./internal/integration/... -count=1.
• go vet ./....
• Mobile screenshot inspected; delete control has a 44×44 touch target.

Closes #119.