feat: add usage daily rollups, incremental auto-vacuum, and sync-aware backup

- Add usage_daily_rollups table (schema v6) to aggregate proxy request
  logs into daily summaries, reducing query overhead for statistics
- Add rollup_and_prune DAO that aggregates old detail logs (>N days)
  into rollup rows and deletes the originals
- Update all usage stats queries to UNION detail logs with rollup data
- Introduce incremental auto-vacuum for SQLite, with startup and
  periodic cleanup of old stream_check_logs and request log rollups
- Split backup export/import into full vs sync variants: WebDAV sync
  now skips local-only table data (proxy_request_logs,
  stream_check_logs, provider_health, proxy_live_backup,
  usage_daily_rollups) while preserving them on import
- Add enable_logging guard to skip request log writes when disabled
- Apply cargo fmt formatting fixes across multiple modules

src-tauri/src/database/tests.rs

@@ -9,6 +9,7 @@ use indexmap::IndexMap;
 use rusqlite::{params, Connection};
 use serde_json::json;
 use std::collections::HashMap;
+use tempfile::NamedTempFile;
 
 const LEGACY_SCHEMA_SQL: &str = r#"
     CREATE TABLE providers (
@@ -633,3 +634,32 @@ fn schema_model_pricing_is_seeded_on_init() {
         gemini_count
     );
 }
+
+#[test]
+fn ensure_incremental_auto_vacuum_rebuilds_existing_file_db() {
+    let temp = NamedTempFile::new().expect("create temp db file");
+    let path = temp.path().to_path_buf();
+
+    let conn = Connection::open(&path).expect("open temp db");
+    conn.execute("PRAGMA auto_vacuum = NONE;", [])
+        .expect("set none auto_vacuum");
+    Database::create_tables_on_conn(&conn).expect("create tables");
+
+    assert_eq!(
+        Database::get_auto_vacuum_mode(&conn).expect("auto_vacuum before rebuild"),
+        0,
+        "existing file db should start with NONE auto_vacuum"
+    );
+
+    let rebuilt =
+        Database::ensure_incremental_auto_vacuum_on_conn(&conn).expect("enable incremental mode");
+    assert!(rebuilt, "existing db should require rebuild via VACUUM");
+    drop(conn);
+
+    let reopened = Connection::open(&path).expect("reopen temp db");
+    assert_eq!(
+        Database::get_auto_vacuum_mode(&reopened).expect("auto_vacuum after rebuild"),
+        2,
+        "file db should persist INCREMENTAL auto_vacuum after VACUUM rebuild"
+    );
+}