fix(settings): align concurrency inputs with host validation limits

[kev1n77]

Summary

Align tool execution concurrency inputs with the host validation limits: 1–32 for subagents and 1–64 for Swarm. Normalize edited values to valid integers and show the host error when saving fails.

Type and Areas

Type: Bug fix

Areas: Web UI settings, tests

Motivation / Impact

The settings UI previously accepted values up to 100, while the host rejected subagent concurrency above 32 and Swarm concurrency above 64. Entering 50 for subagents therefore produced a generic save failure.

Inputs now use the supported bounds, and decimal input is rounded before saving. Failed saves restore the previous value and display the underlying error.

Verification

Validation completed:

• pnpm --dir src/web-ui exec vitest run src/infrastructure/config/components/RuntimeSettingsPages.test.tsx src/infrastructure/config/components/RuntimeSettingsPages.presentation.test.ts — 18 tests passed.
• pnpm run check:web
• git diff --check

Reviewer Notes

• Host limits and runtime scheduling policy are unchanged.
• Existing stored values are preserved on load; normalization applies only when edited.
• Regression coverage includes out-of-range values, decimal input, save rollback, error details, and agreement with the Rust option schema.
• No user-facing translation keys changed.
• Validation used local DOM tests. Remote workspace, remote control, Peer Device Mode, and Detached Dispatch were not exercised end to end.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.