perf(quota): stop recomputing storage usage on every GET /api/auth/me

GET /api/auth/me ran a synchronous O(N) SUM(size) over all the user's
files plus an unconditional UPDATE of auth.users on every call — one of
the most frequently hit endpoints — adding per-request latency, DB write
load, dead tuples and WAL even when nothing changed.

- /api/auth/me now serves the cached storage_used_bytes column instead of
  recomputing it inline.
- New StorageUsageService::start_reconciliation_job runs a periodic sweep
  on the maintenance pool that keeps the cached value current for every
  mutation (uploads, deletes, trash), so freshness no longer depends on
  hitting /me. Interval via OXICLOUD_STORAGE_USAGE_RECONCILE_SECS (default
  600s, floored at 30s; first sweep deferred one interval to avoid boot load).
- update_storage_usage only writes when the value actually changes
  (IS DISTINCT FROM), so the sweep produces no dead tuple / WAL on no-ops.
- New covering partial index idx_files_user_size_active makes the usage
  SUM an index-only scan instead of a heap scan over all the user's files.

Also collapse the same pre-existing clippy collapsible_else_if in
carddav_handler that blocks the -D warnings gate on this base.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/common/config.rs

@@ -211,6 +211,11 @@ pub struct StorageConfig {
     /// Maximum upload file size in bytes (default: 10 GB).
     /// Applied as a hard limit to WebDAV PUT and streaming uploads.
     pub max_upload_size: usize,
+    /// Interval (seconds) of the background sweep that reconciles every user's
+    /// cached `storage_used_bytes` with the real sum of their files. Keeps the
+    /// quota fresh for all mutations without recomputing on the request path.
+    /// Default: 600 (10 min). Env: `OXICLOUD_STORAGE_USAGE_RECONCILE_SECS`.
+    pub usage_reconcile_secs: u64,
     /// Which blob storage backend to use (`local`, `s3`, or `azure`).
     pub backend: StorageBackendType,
     /// S3-compatible backend configuration (used when `backend == S3`).
@@ -348,6 +353,7 @@ impl Default for StorageConfig {
             parallel_threshold: 100 * 1024 * 1024, // 100 MB
             trash_retention_days: 30,              // 30 days
             max_upload_size: MAX_UPLOAD_SIZE,
+            usage_reconcile_secs: 600, // 10 minutes
             backend: StorageBackendType::Local,
             s3: None,
             azure: None,
@@ -1212,6 +1218,14 @@ impl AppConfig {
             config.storage.max_upload_size = val;
         }
 
+        // Background storage-usage reconciliation interval
+        if let Ok(secs) =
+            env::var("OXICLOUD_STORAGE_USAGE_RECONCILE_SECS").map(|v| v.parse::<u64>())
+            && let Ok(val) = secs
+        {
+            config.storage.usage_reconcile_secs = val;
+        }
+
         // Storage backend selection
         if let Ok(backend) = env::var("OXICLOUD_STORAGE_BACKEND") {
             match backend.to_lowercase().as_str() {

src/common/di.rs

@@ -633,6 +633,10 @@ impl AppServiceFactory {
                 user_repository,
             ),
         );
+        // Keep cached storage usage fresh off the request path: GET /api/auth/me
+        // no longer recomputes the O(N) SUM per call; a periodic sweep does it
+        // instead (on the maintenance pool).
+        service.start_reconciliation_job(self.config.storage.usage_reconcile_secs);
         tracing::info!("Storage usage service initialized");
         service
     }