feat(hands): add Creator Hand for media generation (#17)

hands/creator/README.md

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+# Creator Hand
+
+AI media studio -- generates images, videos, music, and speech from natural language prompts.
+
+## Configuration
+
+| Field | Value |
+|-------|-------|
+| Category | `content` |
+| Agents | `creator-hand` (coordinator), `prompt-writer` |
+| Routing | `generate image`, `create video`, `make music`, `text to speech`, `media generation` |
+
+## Integrations
+
+- **OpenAI API** -- Image generation (gpt-image-1, DALL-E 3) and text-to-speech (tts-1).
+- **MiniMax API** -- Image, TTS, video generation (Hailuo T2V-01), and music generation (music-2.5).
+
+## Provider Capabilities
+
+| Provider | Image | TTS | Video | Music |
+|----------|-------|-----|-------|-------|
+| OpenAI | gpt-image-1, dall-e-3 | tts-1, tts-1-hd | -- | -- |
+| MiniMax | image-01 | speech-2.8-hd | T2V-01 | music-2.5 |
+
+## Settings
+
+- **Preferred Provider** -- `auto`, `openai`, `minimax`
+- **Image Model** -- `auto`, `gpt-image-1`, `dall-e-3`, `image-01`
+- **Default Image Size** -- `1024x1024`, `1792x1024`, `1024x1792`
+- **TTS Voice** -- `alloy`, `echo`, `fable`, `nova`, `onyx`, `shimmer`
+- **MiniMax API Key** -- API key from platform.minimaxi.com
+
+## Usage
+
+```bash
+librefang hand run creator
+```
+
+### Examples
+
+```
+> Generate a watercolor painting of a mountain lake at sunrise
+> Create a 5-second video of ocean waves crashing on rocks
+> Make an upbeat electronic jingle, 15 seconds, instrumental
+> Read this text aloud in a warm female voice: "Welcome to..."
+> Make a podcast intro: jingle + voice saying "Welcome to Tech Talk"
+```