CLI: Add agents auth, process resize, and fs watch commands

This PR adds CLI coverage for SDK methods that were previously missing:

## New Commands

### agents auth
- `kernel agents auth list` - List auth agents
- `kernel agents auth get <id>` - Get auth agent details
- `kernel agents auth create` - Create a new auth agent
- `kernel agents auth delete <id>` - Delete an auth agent

### agents auth invocations
- `kernel agents auth invocations create` - Create auth invocation
- `kernel agents auth invocations get <id>` - Get invocation status
- `kernel agents auth invocations submit <id>` - Submit field values

Note: `exchange` is intentionally omitted - it's an internal endpoint for
the hosted UI that uses handoff code auth instead of API keys.

### browsers process
- `kernel browsers process resize <id> <process-id>` - Resize process PTY

### browsers fs watch
- `kernel browsers fs watch start <id>` - Start watching a path
- `kernel browsers fs watch events <id> <watch-id>` - Stream watch events
- `kernel browsers fs watch stop <id> <watch-id>` - Stop watching

Author: masnwilliams