feat(calendar): use global right sidebar in Day view

[h4yfans]

What

Delete the in-page right sidebar (mini calendar + "Today's events") from the Calendar Day view and drive the app's global right sidebar instead. The global sidebar auto-opens when the user enters Day view and auto-closes when leaving — unless the user had opened it manually, in which case it stays open (sticky user intent).

Why

Having two sidebars showing the same information (mini calendar + day events) was redundant and inconsistent. Calendar already relies on the global right sidebar elsewhere; Day view is now aligned with that pattern.

How

• DayPanelContext gains two new actions: openForDayView(date) and closeForDayView(). An internal autoModeRef (non-reactive useRef) tracks whether the current open state came from Day-view auto-open vs. a manual user action. Manual open / close / toggle always clear auto-mode so the user's explicit intent wins.
• openForDayView is a no-op when the panel is already open (preserves the sticky-user-open case). closeForDayView only closes when auto-mode is true.
• CalendarPage wires two small effects: one toggles the panel on view transitions; the other syncs selectedDate to anchorDate while in Day view so the global panel follows Prev/Next/Today navigation.
• CalendarDayView loses its <CalendarMiniMonth> + "Today's events" column, plus the now-dead miniMonthAnchor state and onAnchorChange prop (confirmed dead — shell never forwarded it to Day view).
• The timedItems filter keeps the original toLocalDateKey(startAt) === anchorDate && !isAllDay guard so events spilling in from adjacent days are not rendered on the grid.

Trade-off: chose two useEffects over wiring setDate into every anchorDate mutator (Prev/Next/Today/onAnchorChange). Effects add one lint warning but stay robust if a future change introduces a new anchor-date path.

Type

• feat — new feature
• fix — bug fix
• refactor — restructure without behavior change
• style — visual/UI only
• perf — performance improvement
• test — adding or updating tests
• chore — tooling, deps, config
• docs — documentation only
• ci — CI/CD changes

Test plan

• Unit tests added/updated
• Integration tests added/updated
• Manual testing (describe below)

Manual scenarios to walk through in pnpm dev:

1. Panel starts closed → Navigate to Calendar (Month). Click Day ⇒ global sidebar opens showing anchorDate. Click Week ⇒ closes. Click Day ⇒ opens again.
2. Panel starts manually open (user clicked the global toggle) → Navigate to Calendar. Click Day ⇒ stays open. Click Week ⇒ stays open (sticky). Close manually → click Day ⇒ opens in auto-mode → click Month ⇒ closes.
3. Date sync in Day view → Use Prev/Next/Today; confirm the global sidebar's mini-calendar and day-events follow the calendar's anchorDate.
4. Reload while Day view is auto-open → Panel persists as open via localStorage and is treated as user-opened after reload (safe default); switching to Week keeps it open.

Checklist

• Self-reviewed the diff
• No hardcoded secrets or credentials
• Files stay under ~500 LOC
• Follows immutable data patterns