Add comprehensive documentation and examples

- docs/USAGE.md: Full usage guide with CLI options, Python API, troubleshooting
- docs/ATOMIZER_INTEGRATION.md: Guide for FEA/Atomizer integration
- examples/sample_config.toml: Annotated configuration example
- README.md: Expanded with installation, usage, architecture

examples/sample_config.toml

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+# CAD-Documenter Sample Configuration
+# Copy to ~/.cad-documenter.toml and customize
+
+[api]
+# Vision API provider: "openai" or "anthropic"
+provider = "openai"
+
+# API key - REQUIRED for vision analysis
+# Can also be set via OPENAI_API_KEY or ANTHROPIC_API_KEY environment variable
+# api_key = "sk-your-key-here"
+
+# Model overrides (optional - uses provider defaults if not set)
+# For OpenAI: gpt-4o (default), gpt-4o-mini
+# For Anthropic: claude-sonnet-4-20250514 (default), claude-3-haiku-20240307
+# vision_model = "gpt-4o"
+# text_model = "gpt-4o-mini"
+
+[processing]
+# Whisper model for transcription
+# Options: tiny (fastest), base (default), small, medium, large (most accurate)
+whisper_model = "base"
+
+# Seconds between frame extractions (used if scene detection disabled)
+frame_interval = 2.0
+
+# Use AI-powered scene change detection for smarter frame selection
+use_scene_detection = true
+
+# Maximum frames to analyze (limits API costs)
+max_frames = 15
+
+# Scene detection sensitivity (0.0-1.0, lower = more sensitive)
+scene_threshold = 0.3
+
+[output]
+# Include Bill of Materials table in documentation
+include_bom = true
+
+# Include Atomizer FEA hints section
+include_atomizer_hints = true
+
+# Include raw transcript at end of documentation
+include_raw_transcript = true
+
+# Keep extracted frames in output directory
+include_frames = true
+
+# PDF template name (for future template support)
+pdf_template = "default"