feat(analysis): page-analysis schema, domain types, and analyze_page job kind

Adds the persistence foundation for the AI content-analysis worker:

- Migration 0025: page_analysis (status + scene + is_nsfw + weighted
  search_doc tsvector), page_ocr_text (kind-tagged pieces), global
  page_auto_tags (shared tags vocabulary, separate from per-user
  page_tags), and page_content_warnings (closed vocabulary).
- domain::page_analysis: AnalysisStatus/OcrKind/ContentWarning enums with
  kind->tsvector-weight mapping and lenient model-string parsing, plus the
  VisionAnalysis response DTOs.
- JobPayload::AnalyzePage { page_id, force } + KIND_ANALYZE_PAGE, reusing
  the existing crawler_jobs queue.
- repo::page_analysis: enqueue_for_page, load, mark_failed, and the single
  transactional persist_analysis (delete+reinsert; idempotent; never
  touches user page_tags; computes the A/B/C/D-weighted search_doc).

Tests: repo integration (persist/idempotency/user-tags-untouched/enqueue/
mark_failed/speech>sfx ranking) + unit (weights, parsing, DTO, job serde).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/domain/mod.rs

@@ -7,6 +7,7 @@ pub mod collection;
 pub mod genre;
 pub mod manga;
 pub mod page;
+pub mod page_analysis;
 pub mod page_tag;
 pub mod patch;
 pub mod read_progress;
@@ -26,6 +27,10 @@ pub use collection::{Collection, CollectionPageItem, CollectionSummary};
 pub use genre::{Genre, GenreRef};
 pub use manga::{Manga, MangaCard, MangaDetail};
 pub use page::Page;
+pub use page_analysis::{
+    AnalysisStatus, ContentWarning, OcrKind, OcrResult, PageAnalysis, SafetyFlag,
+    VisionAnalysis,
+};
 pub use page_tag::{
     NewPageTag, PageTagSummary, TaggedChapterAggregate, TaggedMangaAggregate,
     TaggedPageItem,