duplicates: perceptual hash + soft-mark resolution + upload 409

Adds pHash + dHash columns alongside the existing blake3 content_hash so
near-duplicates (re-encoded, resized, format-converted copies) become
queryable. /duplicates/{exact,perceptual} return groups; /duplicates/
{resolve,unresolve} flip a duplicate_of_hash soft-mark on losing rows
and union perceptual-only tag sets onto the survivor. The default
/photos listing filters duplicate_of_hash IS NULL so demoted siblings
stop cluttering the grid; include_duplicates=true opts back in for
Apollo's review modal. Upload now hashes bytes pre-write and returns
409 with the canonical sibling when a file's bytes already exist.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

migrations/2026-05-03-000000_add_perceptual_hash/up.sql

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+-- Adds perceptual-hash signals + soft-mark resolution state to image_exif so
+-- the duplicates surface in Apollo can group near-duplicates (re-encoded,
+-- resized, format-converted copies) and let the user demote losers without
+-- touching the file on disk. Image-only for v1: phash_64/dhash_64 are NULL
+-- on videos and on images that fail to decode. See Apollo CLAUDE.md →
+-- Duplicate detection / Caching layer for the policy.
+--
+-- Soft-mark columns are media-type-agnostic — when video perceptual hashing
+-- arrives, it lives in a separate hash-keyed companion table and reuses the
+-- same duplicate_of_hash / duplicate_decided_at machinery.
+
+-- pHash (DCT, 64-bit) packed as i64 for fast XOR + popcount Hamming.
+ALTER TABLE image_exif ADD COLUMN phash_64 BIGINT;
+
+-- dHash (gradient, 64-bit). Cheap, robust to compression/resize. Stored
+-- alongside pHash so the query layer can fall back if either is null.
+ALTER TABLE image_exif ADD COLUMN dhash_64 BIGINT;
+
+-- When non-null, this row is a soft-marked duplicate of the row whose
+-- content_hash matches. The duplicate file stays on disk; the default
+-- /photos listing filters it out. /photos?include_duplicates=true opts
+-- back in (the Apollo duplicates modal uses this).
+ALTER TABLE image_exif ADD COLUMN duplicate_of_hash TEXT;
+
+-- Unix seconds of the resolve. Distinguishes "never reviewed" from
+-- "reviewed and resolved" for the Apollo include_resolved toggle.
+ALTER TABLE image_exif ADD COLUMN duplicate_decided_at BIGINT;
+
+-- Partial indexes — the columns are NULL for the vast majority of rows
+-- during the transitional window and forever for videos / decode failures.
+CREATE INDEX idx_image_exif_phash
+    ON image_exif (phash_64)
+    WHERE phash_64 IS NOT NULL;
+
+CREATE INDEX idx_image_exif_dhash
+    ON image_exif (dhash_64)
+    WHERE dhash_64 IS NOT NULL;
+
+CREATE INDEX idx_image_exif_duplicate_of_hash
+    ON image_exif (duplicate_of_hash)
+    WHERE duplicate_of_hash IS NOT NULL;