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  matching.go MatchingHandler twins), superseded helpers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

@@ -4,8 +4,6 @@ import { Alpine } from "./alpine";
 import "./admin";
 import "./audio";
 import "./api";
-import "./api-explorer";
-import "./api-explorer-docs";
 import "./bookPicker";
 import "./bookshelf";
 import "./filter_builder";
@@ -17,8 +15,6 @@ import "./custom-section-builder";
 import "./dashboard";
 import "./device-management";
 import "./docs";
-import "./dom";
-import "./events";
 import "./header";
 import "./index";
 import "./library-switcher";
@@ -27,7 +23,6 @@ import "./login";
 import "./password_validation";
 import "./profile";
 import "./profile-modal";
-import "./queue";
 import "./register";
 import "./search";
 import "./series";