fix(dashboard): preserve malformed legacy reasoning_effort on unrelated edits

[dbc-hbin]

Summary

Fixes the dashboard data-loss bug flagged in the #69911 review: a malformed legacy reasoning_effort stored on a cron job was collapsed to null on hydration, and buildCronJobPayload always emitted the key on update — so any unrelated dashboard edit (for example renaming a job) cleared the stored value.

This branch is #69911's feat/cron-reasoning-effort-consolidation head plus one follow-up fix commit, rebased onto the same main.

Problem

cron/jobs.py::update_job treats reasoning_effort as presence-sensitive: an omitted key leaves the stored override unchanged, while null removes it. The web editor always sent reasoning_effort: null for a malformed legacy value (e.g. " turbo "), so a name-only edit destructively removed the stored value — contradicting the read/preserve compatibility contract.

Fix

• web/src/lib/cron-job.ts
  • Hydration now keeps a malformed legacy value as distinct editor state: the raw trimmed string stays in reasoning_effort and preserve_reasoning_on_save is set.
  • buildCronJobPayload omits reasoning_effort from the update payload when the selector was not changed on a malformed legacy value, so unrelated edits preserve it.
  • A valid effort is still always emitted; an explicit selector change still emits null (clear) or the chosen value.
• web/src/pages/CronPage.tsx
  • Changing the reasoning selector clears preserve_reasoning_on_save, so picking "Inherit / default" on a malformed job explicitly clears it.
• web/src/lib/cron-job.test.ts
  • Replaced the test that codified the destructive null rewrite with a name-only edit regression test asserting reasoning_effort is omitted from the payload, plus a test that an explicit selector change still clears the value.

This mirrors the desktop editor's existing reasoningPreserveOnSave semantics in apps/desktop/src/app/cron/cron-job-model.ts.

Verification

• Web Vitest: 102 passed (cron-job suite now 12)
• Web typecheck (tsc -p . --noEmit): passed
• ESLint on changed files: passed
• Web production build: passed

[teknium1]

Same note as #69911 (this branch is its head + a fix): the core cron reasoning-effort half landed on main via #91244 (43c6dac) — the dashboard/desktop/web surfacing plus your malformed-legacy-value preservation fix remain unlanded and still wanted. A rebase onto current main scoped to the UI half + the presence-sensitive update fix would be very welcome; build on _normalize_reasoning_effort/_resolve_job_reasoning_config and keep the field off the model-facing tool schema (policy-pinning test exists).