feat: admin soft-delete and hard-delete for books

- Add `archived` bool to domain.BookMeta, pbBook, and Meilisearch bookDoc
- ArchiveBook / UnarchiveBook patch the PocketBase record; ListBooks filters
  archived=false so hidden books disappear from all public responses
- Meilisearch: add `archived` as a filterable attribute; Search and Catalogue
  always prepend `archived = false` to exclude archived books from results
- DeleteBook permanently removes the PocketBase record, all chapters_idx rows,
  MinIO chapter objects, cover image, and the Meilisearch document
- New BookAdminStore interface with ArchiveBook, UnarchiveBook, DeleteBook
- Admin HTTP endpoints: PATCH /api/admin/books/{slug}/archive|unarchive,
  DELETE /api/admin/books/{slug}
- PocketBase schema: archived field added to live pb.libnovel.cc and to
  pb-init-v3.sh (both create block and add_field migration)

scripts/pb-init-v3.sh

@@ -144,7 +144,8 @@ create "books" '{
     {"name":"total_chapters","type":"number"},
     {"name":"source_url",    "type":"text"},
     {"name":"ranking",       "type":"number"},
-    {"name":"meta_updated",  "type":"text"}
+    {"name":"meta_updated",  "type":"text"},
+    {"name":"archived",      "type":"bool"}
   ]}'
 
 create "chapters_idx" '{
@@ -255,6 +256,7 @@ create "user_settings" '{
     {"name":"font_family",     "type":"text"},
     {"name":"font_size",       "type":"number"},
     {"name":"announce_chapter","type":"bool"},
+    {"name":"audio_mode",      "type":"text"},
     {"name":"updated",         "type":"text"}
   ]}'
 
@@ -389,6 +391,8 @@ add_field "user_settings"  "locale"                 "text"
 add_field "user_settings"  "font_family"            "text"
 add_field "user_settings"  "font_size"              "number"
 add_field "user_settings"  "announce_chapter"       "bool"
+add_field "user_settings"  "audio_mode"             "text"
+add_field "books"          "archived"               "bool"
 
 # ── 6. Indexes ────────────────────────────────────────────────────────────────
 add_index "chapters_idx" "idx_chapters_idx_slug_number" \