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  matching.go MatchingHandler twins), superseded helpers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.

internal/sevenzip/reader.go

@@ -295,30 +295,6 @@ func OpenReader(name string) (*ReadCloser, error) {
 	return OpenReaderWithPassword(name, "")
 }
 
-// NewReaderWithPassword returns a new [*Reader] reading from r using password
-// as the basis of the decryption key, which is assumed to have the given size
-// in bytes.
-func NewReaderWithPassword(r io.ReaderAt, size int64, password string) (*Reader, error) {
-	if size < 0 {
-		return nil, errNegativeSize
-	}
-
-	zr := new(Reader)
-	zr.p = password
-
-	if err := zr.init(r, size); err != nil {
-		return nil, err
-	}
-
-	return zr, nil
-}
-
-// NewReader returns a new [*Reader] reading from r, which is assumed to have
-// the given size in bytes.
-func NewReader(r io.ReaderAt, size int64) (*Reader, error) {
-	return NewReaderWithPassword(r, size, "")
-}
-
 func (z *Reader) folderReader(si *streamsInfo, f int) (*folderReadCloser, uint32, bool, error) {
 	// Create a SectionReader covering all of the streams data
 	return si.FolderReader(io.NewSectionReader(z.r, z.start, z.end-z.start), f, z.p)
@@ -568,17 +544,6 @@ func (z *Reader) init(r io.ReaderAt, size int64) (err error) {
 	return nil
 }
 
-// Volumes returns the list of volumes that have been opened as part of the
-// current archive.
-func (rc *ReadCloser) Volumes() []string {
-	volumes := make([]string, len(rc.f))
-	for idx, f := range rc.f {
-		volumes[idx] = f.Name()
-	}
-
-	return volumes
-}
-
 // Close closes the 7-zip file or volumes, rendering them unusable for I/O.
 func (rc *ReadCloser) Close() error {
 	errs := make([]error, 0, len(rc.f))