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>

example.env

@@ -34,6 +34,13 @@ OXICLOUD_SERVER_HOST=127.0.0.1
 # Maximum upload size in bytes (default: 10 GB on 64-bit)
 #OXICLOUD_MAX_UPLOAD_SIZE=10737418240
 
+# How often (seconds) the background sweep reconciles each user's cached
+# storage usage with the real sum of their files (default: 600 = 10 min).
+# GET /api/auth/me serves the cached value instead of recomputing per request;
+# this sweep keeps it fresh for deletes/trash too. Lower = fresher quota,
+# higher = less background DB work. Minimum enforced: 30s.
+#OXICLOUD_STORAGE_USAGE_RECONCILE_SECS=600
+
 # Allow multiple processes to bind to the same port (SO_REUSEPORT).
 # DISABLED by default — leaving this off means a second accidental instance
 # will fail immediately with "address already in use", which is the safe behaviour.