feat: add skill-seekers video --setup for GPU auto-detection and dependency installation

Auto-detects NVIDIA (CUDA), AMD (ROCm), or CPU-only GPU and installs the
correct PyTorch variant + easyocr + all visual extraction dependencies.
Removes easyocr from video-full pip extras to avoid pulling ~2GB of wrong
CUDA packages on non-NVIDIA systems.

New files:
- video_setup.py (835 lines): GPU detection, PyTorch install, ROCm config,
  venv checks, system dep validation, module selection, verification
- test_video_setup.py (60 tests): Full coverage of detection, install, verify

Updated docs: CHANGELOG, AGENTS.md, CLAUDE.md, README.md, CLI_REFERENCE,
FAQ, TROUBLESHOOTING, installation guide, video dependency plan

All 2523 tests passing (15 skipped).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/getting-started/01-installation.md

@@ -124,10 +124,14 @@ pip install skill-seekers[dev]
 | `gcs` | Google Cloud Storage | `pip install skill-seekers[gcs]` |
 | `azure` | Azure Blob Storage | `pip install skill-seekers[azure]` |
 | `embedding` | Embedding server | `pip install skill-seekers[embedding]` |
+| `video` | YouTube/video transcript extraction | `pip install skill-seekers[video]` |
+| `video-full` | + Whisper transcription, scene detection | `pip install skill-seekers[video-full]` |
 | `all-llms` | All LLM platforms | `pip install skill-seekers[all-llms]` |
 | `all` | Everything | `pip install skill-seekers[all]` |
 | `dev` | Development tools | `pip install skill-seekers[dev]` |
 
+> **Video visual deps:** After installing `skill-seekers[video-full]`, run `skill-seekers video --setup` to auto-detect your GPU (NVIDIA/AMD/CPU) and install the correct PyTorch variant + easyocr.
+
 ---
 
 ## Post-Installation Setup