feat: localize built-in templates and system messages

[borgez]

Summary

• Localize built-in task template names, prompts, checklists, and form prefills using the active GUI language.
• Render host-generated system comments in the active language while retaining their original fallback text, including after JSON export/import.
• Localize the host gitignore hint and template urgency labels.

Validation

• 286 tests passed locally, including localized comment import preservation and validation.
• TypeScript typecheck, host/client build, host smoke test, and client bundle budget check passed.
• GitHub Node.js CI passed before merge.

The scheduler lifecycle test now waits for the expected persisted next-run time; an unloaded store no longer satisfies its completion predicate.