fix(database): create SQLite backup snapshots online (#6137)

* fix(database): snapshot SQLite backups online

Use SQLite's online backup API for downloadable backups and SQLite migration exports instead of checkpointing then reading the live database file. The regression test validates a backup made while writes continue.

* style(database): group SQLite driver imports

* fix(database): bound online backup retries

Use a single backup step and a bounded connection-acquisition/retry context. Tighten temporary-file cleanup and regression assertions while removing the unused checkpoint helper.

* test(database): cover existing backup destinations

* fix(database): harden SQLite snapshot lifecycle

Sweep interrupted snapshot directories at SQLite startup, keep rollback-journal backups incremental, and make caller-owned cleanup explicit. Reuse one scheduled Telegram snapshot across administrators and make the direct SQLite driver dependency explicit.

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Co-authored-by: PathGao <gaoyanbo@gaoyanbodeMacBook-Air.local>

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/websocket v1.5.3
 	github.com/joho/godotenv v1.5.1
+	github.com/mattn/go-sqlite3 v1.14.48
 	github.com/mymmrac/telego v1.11.1
 	github.com/nicksnyder/go-i18n/v2 v2.6.1
 	github.com/op/go-logging v0.0.0-20160315200505-970db520ece7
@@ -68,7 +69,6 @@ require (
 	github.com/leodido/go-urn v1.5.0 // indirect
 	github.com/lufia/plan9stats v0.0.0-20260627054121-477a66015f15 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
-	github.com/mattn/go-sqlite3 v1.14.48 // indirect
 	github.com/miekg/dns v1.1.72 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect