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  matching.go MatchingHandler twins), superseded helpers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/handlers/opds.go

@@ -5,8 +5,6 @@ import (
 	"bookhoard/internal/opds"
 	"bookhoard/internal/services"
 	"context"
-	"crypto/rand"
-	"encoding/hex"
 	"fmt"
 	"net/http"
 	"os"
@@ -1219,57 +1217,3 @@ func (h *OPDSHandler) ListFormats(c *echo.Context) error {
 		"formats":       formatList,
 	})
 }
-
-// RegisterOPDS registers a device for OPDS access
-func (h *OPDSHandler) RegisterOPDS(c *echo.Context) error {
-	deviceID := c.Param("deviceId")
-
-	// Parse device ID
-	deviceUUID, err := uuid.Parse(deviceID)
-	if err != nil {
-		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid device id"})
-	}
-
-	// Verify device exists
-	_, err = h.db.GetDevice(c.Request().Context(), pgtype.UUID{Bytes: deviceUUID, Valid: true})
-	if err != nil {
-		return c.JSON(http.StatusNotFound, map[string]string{"error": "device not found"})
-	}
-
-	// Get base URLs
-	_, opdsBaseURL, err := h.getBaseURLs(c)
-	if err != nil {
-		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "failed to get config"})
-	}
-
-	// Generate OPDS token
-	tokenBytes := make([]byte, 32)
-	if _, err := rand.Read(tokenBytes); err != nil {
-		tokenBytes = []byte(deviceID + "-" + uuid.New().String())
-	}
-	token := hex.EncodeToString(tokenBytes)[:64]
-
-	// Create OPDS token record (valid for 1 year)
-	expiresAt := time.Now().AddDate(1, 0, 0)
-	_, err = h.db.CreateOpdsToken(c.Request().Context(), database.CreateOpdsTokenParams{
-		DeviceID:  pgtype.UUID{Bytes: deviceUUID, Valid: true},
-		Token:     token,
-		TokenType: pgtype.Text{String: "device", Valid: true},
-		ExpiresAt: pgtype.Timestamptz{Time: expiresAt, Valid: true},
-	})
-	if err != nil {
-		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "failed to create OPDS token"})
-	}
-
-	catalogURL := fmt.Sprintf("%s/devices/%s/catalog", opdsBaseURL, deviceID)
-
-	return c.JSON(http.StatusOK, map[string]interface{}{
-		"opds_token": map[string]interface{}{
-			"token":      token,
-			"token_type": "device",
-			"expires_at": expiresAt.Format(time.RFC3339),
-		},
-		"opds_catalog_url": catalogURL,
-		"refresh_interval": 3600,
-	})
-}