refactor: integrate CommandRouter component into chat_loop

Replaced 330+ lines of manual command parsing with CommandRouter-based
enum routing for cleaner, more maintainable code.

Changes:
- Imported CommandType enum for type-safe command routing
- Replaced manual string parsing with command_result.command_type checks
- Converted all command handlers to use CommandRouter pattern:
  * EXIT, HELP, INFO, TEMPLATES, SESSIONS, COMPACT
  * COPY (with query/all/code modes)
  * RESUME, CONTEXT, CLEAR
  * UNKNOWN_COMMAND, TEMPLATE, MULTILINE
  * QUERY (default processing)
- Unified fall-through logic for TEMPLATE/MULTILINE -> QUERY

Benefits:
- Centralized command parsing in well-tested component
- Type-safe command classification with enum
- Easier to add new commands
- Reduced code duplication
- Better separation of concerns

All 510 tests passing, 100% mypy, ruff compliant

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jwesleye