fix: NVIDIA NIM thinking models (kimi-k2.5, deepseek-r1) crash with 400 when tools are present

[Copilot]

NVIDIA NIM returns HTTP 400 when chat_template_kwargs: {thinking: true} and tools are both present in the same request. The agent was unconditionally sending all registered tools to every NVIDIA model, breaking kimi-k2.5 and deepseek-r1 entirely.

Changes

• NVIDIA_THINKING_MODELS constant — module-level Set of models that use thinking: true; replaces duplicate inline definitions
• Tool suppression for thinking models — tools array is omitted from the request body when the model is in NVIDIA_THINKING_MODELS
• Clean system prompt for thinking calls — stores systemPromptStatic (tool-description-free prefix) in agent state; thinking-model calls use this instead of the full prompt, so the model isn't told about tools it can't call
• Missing systemPromptStatic warning — logs to stderr if the static prefix is absent at call time, surfacing initialization issues early

// Before — tools always sent, causes 400 on thinking models
...(toolDefs.length > 0 && { tools: [...] })

// After — mutually exclusive based on thinking capability
const supportsThinking = NVIDIA_THINKING_MODELS.has(model);
...(supportsThinking  && { chat_template_kwargs: { thinking: true } }),
...(!supportsThinking && toolDefs.length > 0 && { tools: [...] }),