Aligns the DingTalk adapter with the env-var bootstrap pattern other
platforms use, and extends inbound handling beyond the `text` msgtype.

Environment variables (gateway/config.py):
- `DINGTALK_CLIENT_ID` / `DINGTALK_CLIENT_SECRET` enable the platform
- `DINGTALK_ALLOWED_USERS` (comma-separated staff ids) populates the
  allow-list under `extra.allowed_users`
- `DINGTALK_HOME_CHANNEL` / `DINGTALK_HOME_CHANNEL_NAME` set the home
  conversation
- `get_connected_platforms` now recognizes DingTalk via `extra.client_id`

Message-type dispatch (gateway/platforms/dingtalk.py):
- DingTalk Stream delivers exactly three chatbot msgtypes: `text`,
  `picture`, `richText`. Dispatch each explicitly and render unknown
  types as a labelled placeholder rather than silently dropping.
- Picture messages map to `MessageType.PHOTO` with `[图片]` placeholder
  (the download API requires an OpenAPI scope this adapter doesn't call).
- `richText` renders each segment: plain text, `@user` mentions, and
  inline pictures as `[图片]`.
- `_extract_text` now takes an explicit `msgtype` to keep callers
  honest; falls back to `message.message_type` when omitted.

Tests updated to cover each dispatch path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…ync process handler

# Conflicts:
#	gateway/platforms/dingtalk.py

Previously the adapter replaced any `picture` or inline `richText` image
with the literal string `[图片]`; vision tools therefore never saw the
actual bytes. This patch exchanges each `downloadCode` for the temporary
CDN URL via `/v1.0/robot/messageFiles/download`, fetches the bytes, and
caches them locally so `MessageEvent.media_urls` points at a real file.

Implementation notes:
- Piggyback on the dingtalk-stream SDK: `register_callback_handler`
  wires `handler.dingtalk_client = stream_client`, which gives us the
  SDK's access-token helper and `get_image_download_url`. Keep the
  handler reference on the adapter (`self._handler`).
- `get_image_download_url` is sync (requests-based) — offload via
  `asyncio.to_thread` to avoid blocking the event loop.
- Failures at any stage (missing code, empty URL, HTTP error) are
  logged but degrade gracefully: the event still dispatches with the
  `[图片]` text placeholder so the agent knows something arrived.
- `message.get_image_list()` handles both `picture` and `richText`
  shapes, so the same path supports inline images in rich messages.
- On successful download the placeholder text is replaced with
  `[图片 × N]` as a short caption alongside the attached media list.

Tests cover: missing handler, single-image success, empty downloadUrl,
partial HTTP failure (continue on remaining codes), and full end-to-end
picture dispatch through `_on_message`.

Depends on NousResearch#8954 (SDK 0.24 async process) and NousResearch#8960 (msgtype dispatch).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Code review feedback on the initial picture-download implementation:

- Hand-rolled httpx.get + cache_image_from_bytes duplicated
  `cache_image_from_url` from gateway/platforms/base.py, which already
  ships retry-with-backoff, SSRF guarding, and magic-byte validation.
  Swap to the shared helper and drop the dependency on `self._http_client`.
- Sequential for-loop serialized N × (token lookup + HTTP) for richText
  messages carrying multiple inline images. Split the per-code work into
  a private `_fetch_one` and fan out via `asyncio.gather`.
- Narrow `except Exception` on the cache step to `(httpx.HTTPError,
  ValueError)` so genuine bugs surface instead of being swallowed.

Tests updated to patch the new `cache_image_from_url` async helper
instead of the previous bytes+http-client combo.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>