fix: schema init, duplicate routes, and image preview bugs

- Move pg_trgm extension creation before CalDAV indexes that depend on it
- Remove duplicate app-password route registration that caused panic
- Fix missing comma in language selector array (Dutch entry)
- Await async canEdit() in file click handler (Promise was always truthy)
- Detect images by extension fallback when mime_type is octet-stream
  (files uploaded via Nextcloud WebDAV API lack correct mime types)

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

db/schema.sql

@@ -6,6 +6,9 @@
 -- All tables use IF NOT EXISTS for idempotent re-runs.
 -- ============================================================
 
+-- ── Extensions required by indexes below ──
+CREATE EXTENSION IF NOT EXISTS pg_trgm;
+
 -- ============================================================
 -- 1. AUTH SCHEMA
 -- ============================================================
@@ -287,10 +290,6 @@ COMMENT ON TABLE caldav.calendar_events IS 'Calendar events (VEVENT) stored with
 COMMENT ON TABLE caldav.calendar_shares IS 'Calendar sharing permissions between users';
 COMMENT ON TABLE caldav.calendar_properties IS 'Custom WebDAV properties on calendars';
 
--- ── pg_trgm extension for GIN trigram indexes (ILIKE / LIKE substring search) ──
--- Required before creating any gin_trgm_ops indexes below.
-CREATE EXTENSION IF NOT EXISTS pg_trgm;
-
 -- ============================================================
 -- 3. CARDDAV SCHEMA (RFC 6352)
 -- ============================================================