feat(repl): implement M12 REPL commands and session tracking
Add comprehensive REPL commands for session management and introspection:
**Session Tracking** (`crates/core/agent/src/session.rs`):
- SessionStats: Track messages, tool calls, tokens, timing
- SessionHistory: Store conversation history and tool call records
- Auto-formatting for durations (seconds, minutes, hours)
**REPL Commands** (in interactive mode):
- `/help` - List all available commands
- `/status` - Show session stats (messages, tools, uptime)
- `/permissions` - Display permission mode and tool access
- `/cost` - Show token usage and timing (free with Ollama!)
- `/history` - View conversation history
- `/clear` - Reset session state
- `/exit` - Exit interactive mode gracefully
**Stats Tracking**:
- Automatic message counting
- Token estimation (chars / 4)
- Duration tracking per message
- Tool call counting (foundation for future)
- Session uptime from start
**Permission Display**:
- Shows current mode (Plan/AcceptEdits/Code)
- Lists tools by category (read-only, write, system)
- Indicates which tools are allowed/ask/deny
**UX Improvements**:
- Welcome message shows model and mode
- Clean command output with emoji indicators
- Helpful error messages for unknown commands
- Session stats persist across messages
**Example Session**:
```
🤖 Owlen Interactive Mode
Model: qwen3:8b
Mode: Plan
> /help
📖 Available Commands: [list]
> Find all Cargo.toml files
🔧 Tool call: glob...
✅ Tool result: 14 files
> /status
📊 Session Status:
Messages: 1
Tools: 1 calls
Uptime: 15s
> /cost
💰 Token Usage: ~234 tokens
> /exit
👋 Goodbye!
```
Implements core M12 requirements for REPL commands and session management.
Future: Checkpointing/rewind functionality can build on this foundation.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
vikingowl
04a7085007