feat(api): SHA-256 and Chromaprint fingerprints for the library (M5.5)

A background Fingerprinter runs after every scan and at startup, one file
at a time, filling media_files.sha256 and track_fingerprints (fpcalc raw,
first 120 s). Without fpcalc only SHA-256 is computed and files stay
queued for Chromaprint. Changing a file's content resets its prints.
Similarity() compares raw prints with a ±80-point alignment search; it is
the basis for duplicate detection in the upload queue.

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

services/api/migrations/00007_fingerprints.sql

@@ -0,0 +1,19 @@
+-- +goose Up
+-- Отпечатки файлов библиотеки для проверки дублей при загрузке (docs/uploads.md#4-проверка-на-дубли):
+-- полный SHA-256 — в media_files.sha256, акустический Chromaprint — здесь.
+ALTER TABLE media_files ADD COLUMN fingerprinted_at timestamptz;
+CREATE INDEX media_files_fingerprint_todo_idx ON media_files (id) WHERE fingerprinted_at IS NULL;
+
+CREATE TABLE track_fingerprints (
+  file_id     uuid PRIMARY KEY REFERENCES media_files(id) ON DELETE CASCADE,
+  duration_ms int NOT NULL,
+  fingerprint int[] NOT NULL, -- raw-отпечаток fpcalc (uint32 как int4)
+  fp_prefix   bigint NOT NULL  -- первые 64 бита — грубый индекс для отбора кандидатов
+);
+CREATE INDEX track_fingerprints_prefix_idx ON track_fingerprints (fp_prefix);
+CREATE INDEX track_fingerprints_duration_idx ON track_fingerprints (duration_ms);
+
+-- +goose Down
+DROP TABLE track_fingerprints;
+DROP INDEX media_files_fingerprint_todo_idx;
+ALTER TABLE media_files DROP COLUMN fingerprinted_at;