feat: xAI image generate/edit, API key import, and per-provider timeouts

- Add dedicated xAI image adapter with generate + edit (multi-image) via
  /v1/images/generations and /v1/images/edits, plus aspect_ratio/resolution UI
- Support importing existing API keys and exposing connection api-key routes
- Add global/per-provider connect timeout overrides from settings
- Keep unrelated provider UX improvements on this branch; no Grok quota tracking

skills/9router-image/SKILL.md

@@ -75,6 +75,7 @@ Common fields above work everywhere. These add/override:
 | Provider | Extra/changed fields | Notes |
 |---|---|---|
 | `openai`, `minimax`, `openrouter`, `recraft` | `quality`, `style`, `response_format` | Standard OpenAI shape |
+| `xai` (Grok Imagine) | `aspect_ratio`, `resolution`, `image`, `images[]` | Generate → `/images/generations`; edit/multi-edit → `/images/edits` (auto when `image`/`images` present). `size` maps to `aspect_ratio`. Up to 3 source images. |
 | `gemini` (nano-banana) | — | Only `prompt`; ignores `size`/`n` |
 | `codex` (gpt-5.4-image) | `image`, `images[]`, `image_detail`, `output_format`, `background` | SSE stream; **ChatGPT Plus/Pro required** |
 | `huggingface` | — | Only `prompt`; returns single image |