Rahulrajaram compaction fixes

[rahulrajaram]

Fix: Conversation overflow, terminal responsiveness, and transcript accuracy

Changes

1. Conversation overflow with token-based compaction

• Fixed bug where message count was used instead of token count, causing overflow errors with large tool outputs
• Track cumulative token usage (input + output) from backend MetadataEvent
• Trigger proactive compaction at 98% of context window based on actual tokens
• Add MetadataEvent support to ChatResponseStream

2. Ctrl+C handling during hook execution

• CLI no longer freezes during "Thinking..." state when hooks are running
• Hooks now respond immediately to Ctrl+C instead of waiting for 30s timeout
• Uses tokio::select! to monitor both hook completion and Ctrl+C signals

3. Transcript sanitization

• Fixed bug where hidden unicode characters appeared in transcript but not in messages sent to LLM
• Moved transcript append to after sanitization step

4. ANSI escape codes in /clear command

• Replaced StyledText helpers with direct crossterm commands for consistent rendering across terminals