Refactor feature flags into semantic groups

[architehc]

Summary

Splits the monolithic extras feature into semantic feature flags for better modularity and faster compile times.

Changes

Split into 8 semantic features:

Feature	Modules	Purpose
tui	tui, demo	TUI dashboard mode with animations
workflows	workflow_dsl, parallel	Workflow automation
resilience	self_healing, degradation	Self-healing capabilities
execution-modes	dry_run, confirm, yolo	Execution control modes
cache	cache	Response caching
log-analysis	log_analysis	Log diagnostics
speculative	speculative	Speculative execution
tokens	tokens	Token management

The extras feature remains as a convenience meta-feature for backward compatibility.

Benefits

• Faster compile times: Enable only needed features
• Smaller binaries: Include only required modules
• Better organization: Clear semantic grouping
• Backward compatible: --features extras still works

Testing

• cargo check --features tui passes
• cargo check --features workflows passes
• cargo check --features extras passes (all features)
• All 100 tests pass
• Clippy clean

🤖 Generated with Claude Code