Support audio, documents, stickers and video notes

Completes TODO #6. The bot accepted photo, animation, video, voice and
sticker; music files, documents and round videos were silently dropped.

- Replace the five near-identical media handlers with one dispatch table.
  Animations are matched before documents because Telegram populates
  both fields for a GIF, so the old ordering would have filed every GIF
  as a document once document support existed.
- Store video notes as "video". Telegram has no cached inline result for
  video notes, so this is what keeps round videos searchable; it costs
  the round presentation on playback.
- Build inline results from a table keyed by media_type, and cover audio
  and document. A test asserts every storable type has a builder, so a
  new media type cannot be added without a way to return it.
- Reuse one MEDIA_FILTER for both the idle and mid-keyword handlers;
  the second list had already drifted from the first.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -1,6 +1,6 @@
 # Memes Bot
 
-A personal Telegram inline bot to store and search media (photos, GIFs, videos, voice) by keywords.
+A personal Telegram inline bot to store and search media (photos, GIFs, videos, voice, music, stickers, files) by keywords.
 
 [فارسی](README.fa.md)
 
@@ -50,7 +50,9 @@ The database will be saved in `./bot_db/media.db`.
 
 ### Usage
 
-**Adding media** — send the bot a photo, GIF, video, or voice message, then type keywords when prompted (comma-separated or one per message), then `/done`.
+**Adding media** — send the bot a photo, GIF, video, voice message, music file, sticker, or any document, then type keywords when prompted (comma-separated or one per message), then `/done`.
+
+Round video messages are stored as regular videos: Telegram has no inline result type for video notes, so keeping them as video is what makes them searchable.
 
 **Searching inline** — in any chat type `@yourbotusername keyword` to search and send.