Add SettingsTab component tests for jobs settings

[selfcontained]

Summary

• Adds apps/web/src/components/app/jobs-settings-tab.test.tsx — 21 jsdom tests pinning the jobs SettingsTab contract, which had no direct component coverage (only jobs-helpers unit tests existed). This closes the Extract shared JobScheduleField and JobAgentTypeField #880 jobs-form-fields follow-up from the recurring test-enforcer job: the extracted JobScheduleField/JobAgentTypeField/option components are now exercised through their real consumer.

What the tests pin

• Save payload contract (exact-object assertions against a single-field-delta base payload): minute→ms conversions, schedule trim-to-null, worktree gating (baseBranch/branchName nulled when unchecked), the keepAgent → autoArchive inversion, and every advanced toggle passthrough.
• Save gating: empty name, invalid cron (error rendered + Save disabled), unparseable timeout minutes.
• Enabled toggle: disabled until a schedule is saved, optimistic set with an exact minimal payload ({name, directory, enabled}), revert + error banner on failure, single-fire while in flight.
• Job identity: unsaved edits survive a same-id refetch (the SSE no-clobber behavior), full reset — including the enabled switch — on job switch.
• Agent type/model: only CLI agent types offered (Terminal filtered), model reset to null on type change.
• Webhook branches and the confirm-gated remove flow (success closes, failure keeps dialog open with the error).

Test design

• Real child tree (jobs-form-fields, BranchSelect, AgentModelSelect) and real react-query model-catalog query; only @/lib/api is mocked.
• 11-mutant battery run against jobs-settings-tab.tsx/jobs-form-fields.tsx — all killed (payload gating, inversion, model reset, CLI filter, showEnabled, reset-effect deps, revert-on-error, enabled reset).
• Reviewed by a general review agent: 0 must-fix, 0 should-fix; 3 hygiene nits applied (gcTime: 0, single-call assertion, clickSave stale-banner guard).

Validation

• pnpm run check ✓
• pnpm --filter @dispatch/web test ✓ (55 files, 697 tests)
• pnpm run finalize:web ✓
• Full suite green before changes: server 2479, inert E2E 178/12 skip, live lane 11 passed

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