feat(simplex): groups, native attachments, text batching, auto-accept

Salvage of PR #27978 cherry-picked onto current main, resolving conflicts
with main's intervening SimpleX plugin fixes (resp-envelope normalization,
health-monitor reconnect-churn fix, bare-form DM addressing).

What's new:
- Group support via SIMPLEX_GROUP_ALLOWED (comma-separated IDs or '*');
  inbound items surface chat_id=group:<id> + chat_type=group. Disabled by
  default so a bot in a group doesn't process every member's traffic.
- Inbound files/voice via rcvFileDescrReady (immediate /freceive) deferred
  through _pending_file_transfers, replayed on rcvFileComplete. Voice notes
  -> MessageType.VOICE.
- Native outbound media: send_image (PNG/JPEG + inline thumbnail), send_voice
  (msgContent.type=voice), send_video, send_document. All addressed by numeric
  ID via /_send ... json [...].
- MEDIA:<path> tags in agent replies stripped and dispatched as voice/document.
- Text-burst batching (HERMES_SIMPLEX_TEXT_BATCH_DELAY, default 0.8s).
- Auto-accept contact requests (SIMPLEX_AUTO_ACCEPT, default true).
- Group send path uses structured /_send #<id> json form (the bracket
  #[<id>] form is parsed as display-name lookup and silently drops).

plugin.yaml bumped to 1.1.0; docs updated. All inside plugins/platforms/simplex/
- no core edits.

Co-authored-by: Juraj Bednar <juraj@bednar.io>

website/docs/user-guide/messaging/simplex.md

@@ -54,8 +54,11 @@ SIMPLEX_HOME_CHANNEL=<contact-id>
 | `SIMPLEX_WS_URL` | Yes | WebSocket URL of the simplex-chat daemon |
 | `SIMPLEX_ALLOWED_USERS` | Recommended | Comma-separated allowlist. Each entry can be a numeric `contactId` **or** a display name — both forms work. |
 | `SIMPLEX_ALLOW_ALL_USERS` | Optional | Set `true` to allow every contact (use carefully) |
-| `SIMPLEX_HOME_CHANNEL` | Optional | Default contact ID for cron job delivery |
+| `SIMPLEX_AUTO_ACCEPT` | Optional | Auto-accept incoming contact requests (default: `true`) |
+| `SIMPLEX_GROUP_ALLOWED` | Optional | Comma-separated group IDs the bot participates in, or `*` for any group. Omit to ignore group messages entirely |
+| `SIMPLEX_HOME_CHANNEL` | Optional | Default contact/group ID for cron job delivery |
 | `SIMPLEX_HOME_CHANNEL_NAME` | Optional | Human label for the home channel |
+| `HERMES_SIMPLEX_TEXT_BATCH_DELAY` | Optional | Quiet-period seconds (default: `0.8`) used to concatenate rapid-fire inbound text messages into one event |
 
 ## Find your contact ID or display name
 
@@ -68,6 +71,37 @@ By default **all contacts are denied**. You must either:
 1. Set `SIMPLEX_ALLOWED_USERS` to a comma-separated list of `contactId`s and/or display names (e.g. `SIMPLEX_ALLOWED_USERS=4,alice` matches either contactId 4 or the contact whose display name is "alice"), or
 2. Use **DM pairing** — send any message to the bot and it will reply with a pairing code. Enter that code via `hermes pairing approve simplex <CODE>`.
 
+## Group chats
+
+By default the adapter ignores group messages — a bot in a group otherwise
+processes every member's traffic. Opt-in explicitly:
+
+```
+SIMPLEX_GROUP_ALLOWED=12,34          # specific group IDs
+# or
+SIMPLEX_GROUP_ALLOWED=*              # any group the bot is in
+```
+
+Address groups by prefixing the chat ID with `group:`, e.g.
+`simplex:group:12` in `send_message` or as a cron `deliver=` target.
+
+## Attachments
+
+The adapter supports native SimpleX attachments in both directions:
+
+- **Inbound** — incoming images, voice notes, and files are accepted via
+  the daemon's XFTP flow (`rcvFileDescrReady` → `/freceive` → wait for
+  `rcvFileComplete`) and surfaced as `MessageEvent.media_urls` with the
+  appropriate `MessageType` (`PHOTO`, `VOICE`, `TEXT` + document).
+- **Outbound** — `send_image_file`, `send_voice`, `send_document`, and
+  `send_video` all use the structured `/_send` form with `filePath`, so
+  the receiving SimpleX client renders images inline and plays voice
+  notes inline rather than offering them as downloads.
+
+Agent replies can also embed `MEDIA:/path/to/file` tags in plain text —
+the adapter strips the tag from the body and sends the file as either a
+voice note (audio extensions) or a document.
+
 ## Using SimpleX with cron jobs
 
 ```python