feat: cleanup hotkeys

[tyler-dane]

Note

Medium Risk
Hotkey handling is refactored from ad-hoc DOM keydown listeners/handlers to useAppHotkey, which can subtly change shortcut scoping and event behavior (focus/typing fields, preventDefault/propagation). Impacts core keyboard flows in the calendar sidebar and grid scrolling.

Overview
Refactors calendar keyboard shortcuts to use the shared useAppHotkey hook instead of component-level onKeyDown/window listeners.

In SomedayEventContainer, Enter-to-edit and Meta+Ctrl+ArrowUp/Down migrations are now registered as focus-gated hotkeys, and SomedayEvent no longer accepts/passes an onKeyDown prop. In useScroll, the "c" shortcut to scroll to “now” is moved to useAppHotkey, and related tests are updated to use fireEvent.focus for focus setup.

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