Add a Custom Bot Type

Custom bot types are currently a code change workflow, not a runtime UI plugin.

Required code changes

Add chart source under control-plane/charts/<bot>/.
Ensure packaging path emits control-plane/internal/service/charts/<bot>.tgz.
Add //go:embed entry and resolver handling in internal/service/charts.go.
Register bot metadata in internal/botenv so install/config UI has env metadata.
Verify install/onboarding handlers support the new bot type.

mise run charts
mise run build
mise run test

Then run clawmachine serve --dev and verify bot appears on /bots/new.