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/proxy/response_processor.rs

@@ -283,6 +283,11 @@ fn create_usage_collector(
     status_code: u16,
     parser_config: &UsageParserConfig,
 ) -> SseUsageCollector {
+    let logging_enabled = state
+        .config
+        .try_read()
+        .map(|c| c.enable_logging)
+        .unwrap_or(true);
     let state = state.clone();
     let provider_id = ctx.provider.id.clone();
     let request_model = ctx.request_model.clone();
@@ -294,6 +299,9 @@ fn create_usage_collector(
     let session_id = ctx.session_id.clone();
 
     SseUsageCollector::new(start_time, move |events, first_token_ms| {
+        if !logging_enabled {
+            return;
+        }
         if let Some(usage) = stream_parser(&events) {
             let model = model_extractor(&events, &request_model);
             let latency_ms = start_time.elapsed().as_millis() as u64;
@@ -358,6 +366,13 @@ fn spawn_log_usage(
     status_code: u16,
     is_streaming: bool,
 ) {
+    // Check enable_logging before spawning the log task
+    if let Ok(config) = state.config.try_read() {
+        if !config.enable_logging {
+            return;
+        }
+    }
+
     let state = state.clone();
     let provider_id = ctx.provider.id.clone();
     let app_type_str = ctx.app_type_str.to_string();