✨ Add content update tools for Studio chat integration

Replace JSON-based chat updates with proper Rig tool implementations.
Iris can now modify commit messages, PR descriptions, and reviews via
tool calls instead of parsing JSON from response text.

Key changes:
- Add UpdateCommitTool, UpdatePRTool, and UpdateReviewTool with channel-based
  communication to the Studio UI
- Migrate debug output from colored println to tracing for cleaner TUI logs
- Switch chat markdown rendering to pulldown-cmark for proper AST parsing
- Remove brittle regex-based JSON extraction from chat response handling
- Enable automatic file logging in Studio mode for debugging

The tool-based approach is more reliable since the LLM explicitly calls
tools rather than embedding JSON that may get malformed or truncated.

Author: hyperb1iss

Cargo.lock

@@ -38,6 +38,7 @@ log = "0.4.27"
 lru = "0.12"
 once_cell = "1.21.3"
 parking_lot = "0.12.1"
+pulldown-cmark = "0.13"
 rand = "0.9.0"
 ratatui = "0.29.0"
 regex = "1.10.6"