Add settings panel with model info, parameters, and tools

[rdwj]

Port the settings panel from the tool-calling-demo. Gear icon in the header opens a slide-out panel showing:

• Model name and defaults (from /v1/agent-info)
• Tunable generation parameters (temperature, max_tokens, top_p, top_k, penalties, reasoning_effort)
• System prompt (read-only)
• Tool list with expandable descriptions

Parameters are sent per-request in the chat completions body. Panel degrades gracefully if /v1/agent-info isn't available.

Reference: tool-calling-demo UI
See UPSTREAM_PORT.md sections 1.1, 1.6, 1.7.