docs: refresh onboarding and add deployment & operations guide

[CJackHwang]

Motivation

• Align repository documentation with the current code paths and runtime behaviour so new users can get the service running and operated reliably.
• Provide a dedicated, detailed deployment and operations guide covering both direct-run and Docker production flows.
• Surface operational guidance for authentication rotation, cookie refreshing and function-calling configuration that matches existing runtime defaults.
• Keep changes to the root README.md minimal and only update the documentation index as a navigational convenience.

Description

• Added a new docs/deployment-and-operations.md that explains deployment modes, production run recommendations, systemd example, Docker instructions, maintenance commands and upgrade procedure.
• Reworked docs/quick-start.md to provide a concise onboarding path: install, initial auth (--debug), daily headless run, minimum validation and a Docker quick path.
• Rewrote docs/configuration-reference.md into grouped sections (Network/Ports, Launch, Auth/Rotation/Cookies, Function Calling, Logging, Timeouts, GUI) and clarified .env defaults vs code fallbacks.
• Expanded docs/api-usage.md to enumerate OpenAI-compatible endpoints plus queue/control and Web UI management APIs; improved docs/auth-rotation-cookie-refresh.md, docs/troubleshooting.md and docs/development-and-release.md with more operational troubleshooting and CI/test guidance.
• Updated docs/README.md and added a single link in the root README.md to the new deployment guide; did not otherwise large-scale modify the root README content.

Testing

• Ran the full test suite with poetry run pytest -q to validate documentation-only changes against the codebase.
• Test run summary: 2381 collected, 2371 passed, 1 failed, 9 skipped (full output available in CI logs).
• The single failing test is tests/integration/test_queue_disconnect.py::test_get_next_request_timeout_real_queue which errored with ModuleNotFoundError: No module named 'api_utils.queue_worker.asyncio'; this appears unrelated to documentation edits.

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