v4.0.0 - 2-Pass Autofix, Speaker Diarization & OpenRouter Gateways

Highlights in v4.0.0

• 2-Pass Hybrid Autofix (--autofix): Combines Whisper-1's frame-accurate timecodes with intelligent LLM context cleanup to correct technical jargon, domain terms, brands, and acronyms in place.
• Automatic Speaker Diarization: Detects and labels speaker turns ([Speaker 1]: ..., [Speaker 2]: ...) during autofix (disable with --no-diarize).
• OpenAI-Compatible Gateways & Models (Issue #1): Full support for OpenRouter, Groq, LiteLLM, vLLM, Deepgram via --model and --base-url.
• Single-Token Auto-Detection: Works seamlessly with just OPENAI_API_KEY (defaults to gpt-5.6-luna) or OPENROUTER_API_KEY (defaults to google/gemini-3.7-flash). Auto-mixes if both keys are set!
• Zero Audio Speedup Distortion: Removed 1.2x speedup filter across all files to preserve 20–50ms acoustic transients and eliminate phonetic blur on foreign terms.