Replace role beads with embedded TOML config files for role definitions.
This is Phase 1 of gt-y1uvb - adds the config infrastructure without
yet switching the daemon to use it.
New files:
- internal/config/roles.go: RoleDefinition types, LoadRoleDefinition()
with layered override resolution (builtin → town → rig)
- internal/config/roles/*.toml: 7 embedded role definitions
- internal/config/roles_test.go: unit tests
New command:
- gt role def <role>: displays effective role configuration
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
