feat(groups): improve dashboard group action feedback

[catwithtudou]

Summary

• Keep the group creation dialog open on validation, network, and API failures, and render the reason inline so users can fix the form and retry.
• Replace the add-bots alert/auto-close flow with inline per-bot results, including partial failures and the no-proxy-bot case.
• Add a small helper test for the add-bots result summary, including escaping ids and backend error text.

Validation

• CI=true npx --yes pnpm@9.5.0 vitest run --project unit test/dashboard-groups-helpers.test.ts
• CI=true npx --yes pnpm@9.5.0 vitest run --project unit test/dashboard-groups-helpers.test.ts test/dashboard-groups-command.test.ts test/groups-card-model.test.ts test/groups-card-dispatch.test.ts
• CI=true npx --yes pnpm@9.5.0 build
• Static Playwright/Chrome smoke for narrow dialog inline-status rendering: no horizontal overflow.

Notes

This PR only changes Dashboard group UI feedback. It does not change group creation, add-bots, or oncall backend behavior.