fix(ui): derive keyboard shortcuts sheet from SHORTCUTS registry

[MattPua]

Problem

The keyboard shortcuts modal and command palette showed different shortcuts — they were two independently hand-maintained lists that had drifted. E.g. RELOAD_WINDOW was bound and shown in the command palette but missing from the modal.

Changes

KEYBOARD_SHORTCUTS (the modal's data) is now derived from SHORTCUTS (the map already used everywhere for actual hotkey binding), via a SHORTCUT_META description map. Adding a new SHORTCUTS entry now fails to compile unless it's documented or explicitly excluded (HIDDEN_FROM_SHEET), so the two surfaces can't silently drift again.

Editor-keymap shortcuts (Tiptap bold/italic/etc.) that don't go through SHORTCUTS are kept as a small hand-written list, since there's no single source to derive them from.

How did you test this?

• pnpm --filter @posthog/ui typecheck — passes
• Added keyboard-shortcuts.test.ts asserting every bound key is documented in the sheet — passes
• Ran full command test suite — 34 tests passing

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 3a3a3d6.}