feat(metadata): SQLite backend, storage reconciliation and local defaults

- pluggable per-domain Repository interfaces; PostgreSQL and SQLite impls
- SQLite on modernc.org/sqlite (WAL, busy_timeout, foreign_keys, immediate tx)
- separate migrations/sqlite and db.MigrateSQLite; store.NewPostgres/NewSQLite
- cmd/reconcile compares object storage with the journal (report, then --delete)
- storage.Backend.List and photos.Repository.AllStorageKeys
- DB_BACKEND/SQLITE_PATH and STORAGE_BACKEND/FS_ROOT selectable; local defaults
  (sqlite ./galo.db, fs ./data)
- Makefile reconcile/reconcile-delete; docs and .env.example updated

backend/go.mod

@@ -17,6 +17,7 @@ require (
 	github.com/google/uuid v1.6.0
 	github.com/jackc/pgx/v5 v5.11.0
 	golang.org/x/crypto v0.58.0
+	modernc.org/sqlite v1.60.1
 )
 
 require (
@@ -39,6 +40,7 @@ require (
 	github.com/cloudwego/base64x v0.1.6 // indirect
 	github.com/dsoprea/go-logging v0.0.0-20200710184922-b02d349568dd // indirect
 	github.com/dsoprea/go-utility/v2 v2.0.0-20221003172846-a3e1774ef349 // indirect
+	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/ebitengine/purego v0.10.1 // indirect
 	github.com/gabriel-vasile/mimetype v1.4.12 // indirect
 	github.com/gin-contrib/sse v1.1.0 // indirect
@@ -56,12 +58,14 @@ require (
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/klauspost/cpuid/v2 v2.3.0 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
-	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/mattn/go-isatty v0.0.24 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
 	github.com/quic-go/qpack v0.6.0 // indirect
 	github.com/quic-go/quic-go v0.59.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.3.1 // indirect
 	go.mongodb.org/mongo-driver/v2 v2.5.0 // indirect
@@ -73,4 +77,7 @@ require (
 	golang.org/x/text v0.43.0 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
+	modernc.org/libc v1.77.1 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.12.1 // indirect
 )