feat: open the dashboard that fits the time of day and device

[AmrMsCLL]

Stacked on #47. This is 11e of as2026-10-05-strata-phase-11-next-batch-2.md.

What changes

• While editing a dashboard, "Opens by itself" sets a time range and a device: any device, phones or computers. A range can cross midnight, for example 22:00 to 06:00.
• Home opens the first dashboard whose time and device match. Dashboards with conditions win over plain ones, and the first dashboard is the fallback. Phones are screens narrower than 768px, the same breakpoint as the tab bar.
• Choosing a dashboard by hand is remembered for the rest of the visit in sessionStorage. If storage is unavailable, Home falls back to the automatic choice.
• Saving sends the schedule only when it changed.

Migration

20261005120000_dashboard_context:

ALTER TABLE "dashboards" ADD COLUMN "show_from" INTEGER,
ADD COLUMN "show_until" INTEGER,
ADD COLUMN "show_on" TEXT NOT NULL DEFAULT 'any';

Contract

• Dashboards gain showFrom and showUntil (minutes after midnight, or null) and showOn (any, phone or desktop). PATCH /me/dashboards/:id accepts all three; the two times must be set together and must differ.

Verification

• Server integration: test/integration/dashboards.spec.ts (2 passed).
• Frontend: test/dashboard.spec.tsx (7 passed). It covers the picker, including a range crossing midnight, and the edit flow.
• Lint and build pass.