fix: filter the pile on chat flags and fetch snippets from the message index

Verified against Beeper Desktop 4.3.73 with a real token:

- inbox=primary combined with unreadOnly=true returned 0 of 78 genuinely
  unread chats, and includeMuted=false returned muted chats anyway. Both
  params are gone; muted/archived/low-priority are now decided here from
  isMuted/isArchived/isLowPriority, and a hand-marked-unread chat counts.
- Snippets now come from GET /v1/messages/search (1.1 ms/chat) instead of
  GET /v1/chats/{id}/messages (145 ms/chat), which is kept as the fallback
  for chats the index has not reached. list --limit 50 went 3.33s -> 0.16s.

docs/SETUP.md

@@ -17,14 +17,15 @@ its settings.
 
 In Beeper Desktop: **Settings → Integrations → create an access token.**
 
-Read access is all this plugin needs. It calls exactly six endpoints:
+Read access is all this plugin needs. It calls exactly seven endpoints:
 
 | Call | Why |
 | --- | --- |
 | `GET /v1/info` | Tell "Beeper is down" apart from "the token is wrong" |
 | `GET /v1/accounts` | Network names for the chips, and the account count |
-| `GET /v1/chats/search` | The unread pile |
-| `GET /v1/chats/{chatID}/messages` | The last message, for the row snippet |
+| `GET /v1/chats/search` | The unread pile (`unreadOnly=true`) |
+| `GET /v1/messages/search` | The last message of a visible row, for the snippet |
+| `GET /v1/chats/{chatID}/messages` | Snippet fallback for a chat the index has not reached |
 | `POST /v1/chats/{chatID}/read` | Mark a chat read |
 | `POST /v1/focus` | Bring Beeper Desktop forward on a chat |