[Fix] Session reminders fail when users request a delay in seconds

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

Related issue

Follow-up to merged #2239. No linked issue.

Why this PR exists

• A maintainer explicitly invited this PR in the linked issue or discussion
• I am a maintainer / this is internal Roomote work

Second-based reminders were rejected by the minute/hour/day-only grammar. This fixes requests such as "say something in 30 seconds" without accepting fractional or compound textual durations.

What changed

• Accept in 30s and seconds aliases for one-shot reminders, and every 30s x3 for bounded recurring checks. Recurring intervals under five minutes still require a run count or end time; cron stays five-field.
• Preserve existing JSONB minute fields, storing whole seconds as canonical fractional minutes. Existing whole-unit schedules and legacy absolute rows retain their behavior and deduplication identity; no migration is needed.
• Validate positive whole-second durations and existing maximum horizons, round timestamp arithmetic to milliseconds, and display fractional-minute intervals as seconds.
• Update the shared native tool grammar/descriptions, Fast prompt guidance, and public docs to use in 30s, not in 0.5m.

Delivery remains best effort. Queue infrastructure and the one-minute lost-hint recovery sweep are unchanged; no exact-time delivery guarantee is introduced.

How it was tested

• Targeted Vitest: 59 cloud-agents parser/schedule/service tests, 10 shared contract tests, 16 real-PostgreSQL wakeup tests, and 101 SDK firing/parent-event tests pass (186 total).
• New real-DB native-handler tests verify persistence at now + 30 seconds, the queue hint timestamp, default report policy, retry deduplication across clock changes/equivalent units, and no persistence or queueing on invalid text. The queue boundary is mocked; this is not a live delivery test.
• pnpm lint:fast, pnpm check-types:fast, pnpm knip, focused formatting, git diff --check, and docs validation/link checks pass. Commit and full pre-push hooks pass. A non-failing Knip configuration hint about mint remains.
• Browser proof is not applicable to this parsing/scheduling/docs change. No live provider/model reminder delivery was tested. Nothing was merged or deployed.

Checklist

• The PR title follows the repo convention: [Fix], [Feat], [Improve], [Refactor], [Docs], or [Chore] followed by a user-facing description
• This PR is small and scoped to one change
• pnpm lint and pnpm check-types pass locally
• I added tests or included a clear manual validation note above
• I removed secrets, tokens, private keys, and customer data from code, logs, and screenshots
• If this change should appear in the changelog, I ran pnpm changeset

The fast static gates listed above were run instead of the full formatting-inclusive commands. No changeset was added.

[roomote-community]

No code issues found. See task

_{Reviewed 0263d64}