feat(versions): schema and VersionDao for hash-keyed photo versions

photo_versions links a version's content_hash to its primary original's;
photo_version_references keeps provenance-only reference photos;
photo_version_display holds the global display choice. VersionDao covers
linking (chains flatten to the root), the display choice, per-original
summaries for /photos, the hidden-row set for non-SQL listings, and the
copy of the original's date/GPS/camera onto version rows. Also the SQL
predicate listings use to hide a version while its original is reachable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

migrations/2026-10-30-000000_add_photo_versions/down.sql

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+DROP TABLE IF EXISTS photo_version_display;
+DROP TABLE IF EXISTS photo_version_references;
+DROP TABLE IF EXISTS photo_versions;

migrations/2026-10-30-000000_add_photo_versions/up.sql

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+-- Photo versions (#191): an AI restoration, upscale or edit that sits on
+-- disk near its original and is shown as the *same photo*.
+--
+-- The link is hash-keyed like every other derived table (CLAUDE.md →
+-- "Multi-library data model"): a version records the blake3
+-- `content_hash` of its primary original, so the link survives moves,
+-- renames and an archive handoff. File name and location are hints only.
+-- The version keeps its own `image_exif` row, so it still downloads and
+-- thumbnails on its own; listings hide it while its original is reachable
+-- in the current view (same rule as `duplicate_of_hash`).
+
+-- A file is a version of at most one original.
+CREATE TABLE photo_versions (
+    version_hash  TEXT PRIMARY KEY NOT NULL,
+    original_hash TEXT NOT NULL,
+    kind          TEXT NOT NULL,      -- restored | upscale | edit
+    source        TEXT NOT NULL,      -- xmp | name | backfill | api
+    created_at    BIGINT NOT NULL,
+    -- Denormalized back-ref to a live image_exif row for the version, kept
+    -- current by the back-ref refresh pass (same pattern as face_detections).
+    library_id    INTEGER NOT NULL,
+    rel_path      TEXT NOT NULL
+);
+CREATE INDEX idx_photo_versions_original ON photo_versions(original_hash);
+
+-- Reference photos (extra context fed to the model). Provenance only: a
+-- reference is never hidden or grouped because of the version.
+CREATE TABLE photo_version_references (
+    version_hash   TEXT NOT NULL,
+    reference_hash TEXT NOT NULL,
+    PRIMARY KEY (version_hash, reference_hash)
+);
+CREATE INDEX idx_photo_version_references_ref ON photo_version_references(reference_hash);
+
+-- The global (not per-user) choice of which file represents a photo.
+-- No row = show the original.
+CREATE TABLE photo_version_display (
+    original_hash TEXT PRIMARY KEY NOT NULL,
+    display_hash  TEXT NOT NULL,
+    decided_at    BIGINT NOT NULL
+);