fix: raise gunicorn request line limit to keep tags API working with hundreds of knowledge bases

[Jackkp0t]

What

Set gunicorn --limit-request-line to 8190 bytes (the maximum it accepts) in apps/common/management/commands/services/services/gunicorn.py, instead of relying on the 4094-byte default.

Why

The search-document workflow node fetches its tag options on page load via

GET /workspace/<workspace_id>/knowledge/tags?knowledge_ids[]=<uuid>&knowledge_ids[]=<uuid>&...

(ui/src/workflow/nodes/search-document-node/index.vue watches knowledge_id_list and calls getAllTags with the node's full list; axios serializes the array as repeated knowledge_ids[]= params, which the backend reads via request.query_params.getlist('knowledge_ids[]').)

With hundreds of associated knowledge bases each knowledge_ids[]=<uuid> param adds ~58 bytes, so the request line reaches ~5,766 bytes at 100 ids. Production runs gunicorn (docker entrypoint python main.py start → GunicornService), whose default limit_request_line is 4094 bytes; over-limit request lines are answered with HTTP 400 (workers/base.py: handle_error maps LimitRequestLine to status_int = 400). The tag dropdown therefore shows 无数据 exactly as reported in #7199. Dev mode uses Django runserver, which has no such limit — which is why it doesn't reproduce locally.

8190 bytes covers ~140 knowledge base ids and also protects other legitimate long-GET endpoints.

How verified

• Red/green against the real gunicorn 23.0.0 parser source (the pinned version, gunicorn/http/message.py + errors.py): with the default 4094, a 100-id request line (5,766 bytes) raises LimitRequestLine → HTTP 400 (Request Line is too large (5766 > 4094)); with 8190 the same request parses and yields all 100 params. Also verified at 140 ids / 8,046 bytes.
• python -m py_compile passes; ruff check / ruff format --check findings on this file are byte-identical to the upstream baseline (pre-existing star-import F403/F405 and formatting), i.e. zero new findings from this change.

Closes #7199

[liuruibin]

It can't solve the problem, it only delays it.