storage: add upload_files table and UploadRepo

Add the upload_files SQLite table and UploadRepo CRUD methods

(Create/Get/List/Delete). The table stores file_id, name, size,

sha256, and uploaded_at as a queryable index.

The .meta.json sidecar remains the source of truth for uploads;

the DB is only an index for admin visibility. On startup the next

commit will backfill any pre-existing sidecars into this table.

Tests cover Create/Get/List/Delete round-trip, name search

filtering, descending time ordering, and limit defaults/cap.

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

internal/storage/sqlite.go

@@ -38,6 +38,15 @@ CREATE TABLE IF NOT EXISTS audit_log (
   details     TEXT
 );
 CREATE INDEX IF NOT EXISTS idx_audit_ts ON audit_log(timestamp DESC);
+
+CREATE TABLE IF NOT EXISTS upload_files (
+  file_id      TEXT PRIMARY KEY,
+  name         TEXT NOT NULL,
+  size         INTEGER NOT NULL,
+  sha256       TEXT NOT NULL,
+  uploaded_at  INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS idx_uploads_ts ON upload_files(uploaded_at DESC);
 `
 
 // DB is the storage handle.