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>

src/database/schema.rs

@@ -121,6 +121,10 @@ diesel::table! {
         last_modified -> BigInt,
         content_hash -> Nullable<Text>,
         size_bytes -> Nullable<BigInt>,
+        phash_64 -> Nullable<BigInt>,
+        dhash_64 -> Nullable<BigInt>,
+        duplicate_of_hash -> Nullable<Text>,
+        duplicate_decided_at -> Nullable<BigInt>,
     }
 }