feat: add video analyzer tool with FFmpeg + subtitle support

[NSIETeam]

What

Adds a new analyze_video tool that downloads, analyzes, and summarizes videos.

Features

• Download: yt-dlp for YouTube/Zoom/Loom, curl for direct URLs, local file support
• Key frame extraction: FFmpeg scene detection (0.4 threshold), falls back to uniform sampling
• Subtitles: YouTube official auto-subs first, Whisper transcription as fallback
• LLM analysis: Sends frames + subtitles to vision model for structured summary (topics, key moments, action items)
• Knowledge base: Optionally saves analysis to ~/.easycode/kb/videos/ for future recall

Dependencies

• yt-dlp (video download)
• ffmpeg + ffprobe (frame extraction + duration)
• whisper (optional, for non-YouTube subtitle transcription)

Origin

Ported from Otto. Adapted for EasyCode:

• Removed SceneType, getResponseText, isCustomModel dependencies
• Simplified LLM analysis: uses config.getOttoClient() if available, falls back to basic summary
• Changed temp/kb dirs from ~/.otto/ to ~/.easycode/