feat: add SQLite storage for login attempts and sessions

Adds persistent storage using modernc.org/sqlite (pure Go). Login
attempts are deduplicated by (username, password, ip) with counts.
Sessions and session logs are tracked with UUID IDs. Includes embedded
SQL migrations, configurable retention with background pruning, and
an in-memory store for tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

go.mod

@@ -3,7 +3,20 @@ module git.t-juice.club/torjus/oubliette
 go 1.25.5
 
 require (
-	github.com/BurntSushi/toml v1.6.0 // indirect
-	golang.org/x/crypto v0.48.0 // indirect
-	golang.org/x/sys v0.41.0 // indirect
+	github.com/BurntSushi/toml v1.6.0
+	github.com/google/uuid v1.6.0
+	golang.org/x/crypto v0.48.0
+	modernc.org/sqlite v1.45.0
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
+	golang.org/x/sys v0.41.0 // indirect
+	modernc.org/libc v1.67.6 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
 )