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  matching.go MatchingHandler twins), superseded helpers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/api.ts

@@ -90,18 +90,6 @@ interface ReadingProgress {
   percentage?: number;
   last_read_at: string;
 }
-async function getReaderMetadata(mediaItemId: string): Promise<ReaderMetadata> {
-  const response = await apiGet(`/media-items/${mediaItemId}`);
-  return handleResponse<ReaderMetadata>(response);
-}
-async function updateReadingProgress(
-  mediaItemId: string,
-  progress: ReadingProgress,
-): Promise<void> {
-  const response = await apiPut(`/media-items/${mediaItemId}/progress`, progress);
-  await handleVoidResponse(response);
-}
-
 async function getReadingProgress(mediaItemId: string): Promise<ReadingProgress | null> {
   const response = await apiGet(`/media-items/${mediaItemId}/progress`);
 
@@ -117,14 +105,10 @@ export {
   apiPost,
   apiPut,
   apiDelete,
-  apiPatch,
   handleResponse,
   handleVoidResponse,
   handleError,
-  getReaderMetadata,
   getReadingProgress, // ADD THIS
-  updateReadingProgress,
-  ReadingProgress,
 };
 
 Alpine.data("api", () => ({