docs: correct the schema, API flow, tool calling and monitoring reference pages against the current code

[silentoplayz]

Summary

I compared the database schema, API flow, server-side tool calling and monitoring reference pages with the models, the chat completion path and the telemetry code.

• Schema: access_grant.id is a Text UUID, not an autoincrement integer, and its created_at is NOT NULL. The old_chat column is dropped by the same migration that creates it. knowledge.data is an unused leftover. DATABASE_ENABLE_SQLITE_WAL defaults to True, and DATABASE_POOL_MAX_OVERFLOW is added.
• API flow: POST /api/chat/completions inserts the assistant placeholder itself for an existing chat, linked under the user_message it is sent; a pre-created placeholder keeps its parent only when user_message is sent too. With session_id and chat_id present, it runs as a background task and returns {status, task_ids, chat_id} rather than streaming. The chat update merge is per message, not per field.
• Tool calling: the completion endpoint can create the chat and placeholder itself, and the manual steps remain as an option; the A2 and Python examples now send user_message, without which the pre-created placeholder loses its parent.
• Monitoring: /health returns {"status": true} unconditionally, so the page now points at /health/db and /ready. The OTel page names the eight instrumentation packages the setup imports and the real code defaults outside the Compose file. It also names the gRPC versus HTTP exporter switch, the fact that only the sync engine is instrumented for SQLAlchemy, the three user gauges, and the logging instrument.

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Sources on dev: models/access_grants.py, migrations/versions/242a2047eae0_update_chat_table.py, models/knowledge.py, env.py (DATABASE_ENABLE_SQLITE_WAL, DATABASE_POOL_*, OTEL_*), main.py (placeholder insertion, the fan-out branch, /health, /ready, /health/db, setup_opentelemetry(db_engine=engine)), models/chats.py (merge_history), utils/telemetry/instrumentors.py and metrics.py, and backend/requirements.txt. The branch is rebased on main, which has since replaced the schema page's SQLCipher section.