security: fix vulnerabilities 1-7 from security audit

- Fix #1: Share handler IDOR - enforce owner check on share operations
- Fix #2: list_files_query IDOR - bind folder queries to authenticated user
- Fix #3: Dedup handler IDOR - restrict dedup operations to file owner
- Fix #4: Trash handler OptionalAuthUser - require full AuthUser
- Fix #5: Error info leakage - sanitize 500 error responses
- Fix #6: Chunked upload IDOR - bind upload sessions to user_id,
  add verify_session_owner() check on all session operations
- Fix #7: CSP unsafe-inline removal - migrate all inline scripts,
  styles and event handlers to external files, tighten CSP to
  script-src 'self'; style-src 'self'

New files:
  - static/js/core/theme-init.js (render-blocking theme init)
  - static/js/core/sw-register.js (service worker registration)
  - static/css/views/device-verify.css (extracted inline styles)
  - static/js/views/device-verify/device-verify.js (extracted inline script)

static/css/components/spinner.css

@@ -40,6 +40,11 @@
 	display: none;
 }
 
+.dropzone-icon {
+	font-size: 32px;
+	margin-bottom: 10px;
+}
+
 .dropzone.active {
 	border-color: #ff5e3a;
 	background-color: rgba(255, 94, 58, 0.05);