refactor: remove dead code across server, templ pages, and client modules

Deadcode-verified removals (RTA reachability from main, cross-checked
with -test and textual xrefs):

Go server:
- whole files: middleware/transaction.go, middleware/error_handler.go,
  middleware/password_validator.go (live registration machinery kept),
  handlers/sync.go, sync/offline.go
- unrouted endpoints: auth UpdateUsername/UpdateEmail, timezone
  settings handler, OPDS RegisterOPDS, Kobo LibrarySync handler,
  ReaderHandler.ShowReader, JSON-data twins on collections/library
- duplicate book-matching handlers (book_matching.go Handler twins,
  matching.go MatchingHandler twins), superseded helpers
  (router.parseUUID, handlers.ValidateDeviceToken, normalizePath,
  userExists, generateLockID)

Templ/client:
- never-routed pages: api_explorer.templ, queue.templ and their
  client modules api-explorer.ts, api-explorer-docs.ts, queue.ts
- fully orphaned wrapper modules events.ts, dom.ts
- broken clearSyncQueue (called a nonexistent endpoint) and the
  hidden, never-populated sync-queue section on the devices page
- 166+ unused exports demoted to private (knip-verified); ~85 truly
  dead declarations removed via tsc noUnusedLocals fixpoint
- stale 'interactive API Explorer' claims dropped from docs

The docs drift-gate package (internal/docs), templ-bound modules
(dashboard, stats, header, index, login, profile*, bookshelf,
collections, toast-error), sqlc-generated code, and web/static are
intentionally untouched.

web/src/device-management.ts

@@ -533,29 +533,6 @@ async function rejectDevice(registrationId: string): Promise<void> {
   }
 }
 
-async function clearSyncQueue(): Promise<void> {
-  if (!confirm("Are you sure you want to clear all sync queue items?")) return;
-
-  const token = getToken();
-  if (!token) return;
-
-  try {
-    const response = await fetch("/api/queue/clear", {
-      method: "DELETE",
-      headers: { Authorization: `Bearer ${token}` },
-    });
-
-    if (response.ok) {
-      showToast("Sync queue cleared", "success");
-    } else {
-      showToast("Failed to clear queue", "error");
-    }
-  } catch (error) {
-    console.error("Failed to clear queue", error);
-    showToast("Failed to clear queue", "error");
-  }
-}
-
 function setupEventDelegation(): void {
   document.addEventListener("click", (e) => {
     const target = e.target as HTMLElement;
@@ -578,34 +555,8 @@ function setupEventDelegation(): void {
   });
 }
 
-export {
-  approveDevice,
-  clearSyncQueue,
-  copyToClipboard,
-  deleteMapping,
-  editMapping,
-  getDeviceIcon,
-  handleAddDevice,
-  handleRevokeDevice,
-  handleSaveDeviceSettings,
-  handleSaveMapping,
-  hideAddDeviceModal,
-  hideAddMappingModal,
-  hideDeviceSettingsModal,
-  hideShelfMappingsModal,
-  loadCollections,
-  loadShelfMappings,
-  rejectDevice,
-  setupEventDelegation,
-  showAddDeviceModal,
-  showAddMappingModal,
-  showDeviceSettings,
-  showShelfMappings,
-};
-
 Alpine.data("devices", () => ({
   approveDevice,
-  clearSyncQueue,
   copyToClipboard,
   deleteMapping,
   editMapping,