fix(auth): update PocketBase v0.23+ auth endpoint and rename users collection

- Replace deprecated /api/admins/auth-with-password with
  /api/collections/_superusers/auth-with-password in both the
  SvelteKit UI (pocketbase.ts) and Go scraper (pocketbase.go)
- Rename custom users collection to app_users to avoid name clash
  with PocketBase's built-in users auth collection
- Fix docker-compose volume mount path pb/pb_data -> pb_data so
  persisted data matches the entrypoint --dir flag
- Add PB_ADMIN_EMAIL/PB_ADMIN_PASSWORD env vars to pocketbase service
  so the superuser is auto-created on first boot

scraper/internal/storage/pocketbase.go

@@ -9,7 +9,7 @@
 //	ranking_html — page(number,unique), html(text), updated(date)
 //	progress     — session_id(text), slug(text), chapter(number), updated(date)
 //	audio_cache  — cache_key(text,unique), filename(text), updated(date)
-//	users        — username(text,unique), password_hash(text), role(text), created(date)
+//	app_users    — username(text,unique), password_hash(text), role(text), created(date)
 package storage
 
 import (
@@ -60,7 +60,7 @@ func (p *pbClient) authenticate(ctx context.Context) error {
 		"password": p.cfg.AdminPassword,
 	})
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
-		p.cfg.BaseURL+"/api/admins/auth-with-password", bytes.NewReader(body))
+		p.cfg.BaseURL+"/api/collections/_superusers/auth-with-password", bytes.NewReader(body))
 	if err != nil {
 		return err
 	}
@@ -314,7 +314,7 @@ func (s *PocketBaseStore) EnsureCollections(ctx context.Context) error {
 			},
 		},
 		{
-			"name": "users",
+			"name": "app_users",
 			"type": "base",
 			"schema": []map[string]interface{}{
 				{"name": "username", "type": "text", "required": true, "options": map[string]interface{}{"min": 3, "max": 32}},