feat(opds): add catalog navigation and search

[phildenhoff]

Why

Until now the catalog was a flat root feed plus acquisition pages: a reader could page through books but couldn't browse by author, series, or tag, and there was no search at all. KOReader in particular expects an OpenSearch description before it will offer its search UI.

What changed

• Navigation feeds for all books, recently modified, and unread, plus author/series/tag facet feeds with per-facet book counts, each paginating into the existing acquisition machinery. The root is a proper navigation feed now.
• A Genres entry exists in the navigation but returns an empty facet for now — it lights up when the canonical-genres layer lands on top of this.
• /opds/search?q=… backed by a new libcalibre text query, capped at 200 characters, and /opds/opensearch.xml so readers can discover it.
• libcalibre gains the facet listings and filtered book-page queries behind BookQuery.

Validation: the stack tip runs 62 citadel-opds tests + 348 workspace tests, all green. The headless process test now also walks the navigation feed and /opds/all.

Stack: #146 → #147 → #148 → #149 → #150 → #151 → #152 (this) → #153 → #154 → #155

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.69%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.69%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.69%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.

[github-actions]

libcalibre Test Coverage Report

Overall coverage: 83.85%

📊 Download HTML Report

Coverage breakdown available in the artifacts.