release: 1.3.4 - Robust Shutdown & Context Injection

[matty-drexler]

This release incorporates:

1. Robust Shutdown Logic: Explicit handling for SIGINT, SIGTERM, and stdin closure to prevent directory locks during updates.
2. Multi-Company Context: Automatic injection of allowed company IDs for cross-company visibility.
3. Safety Interceptors: Auto-detection of HTML in chatter messages.
4. Enhanced Diagnostics: Improved error formatting to expose business logic failures for agent self-correction.
5. Release Workflow: Documented official release procedures in GEMINI.md.