fix(sidebar): keep the peeked sidebar open while the ProjectSwitcher menu is open

[aleexzxzxzx]

Problem

Closes #3483

The collapsed-sidebar hover-peek (#3367) closes the peek on any directional exit,
including while the ProjectSwitcher menu is open. That menu renders in a portal
anchored to its trigger inside the sidebar, so when the peek collapses the menu is
left floating over the content, chasing its vanished anchor. Its submenus
(Project, Organization) fly out to the right, past PEEK_CLOSE_MARGIN, so
hovering them triggers the same close.

Changes

Add a "hold" to sidebarPeekStore: while a sidebar-spawned menu is open,
endSidebarPeek is a no-op, so a pointer that leaves the panel can't collapse the
peek and strand the open menu's anchor.

• holdSidebarPeek() / releaseSidebarPeek() guard a module-level held flag;
  endSidebarPeek early-returns while held, and cancelSidebarPeek clears it.
• ProjectSwitcher holds on open and releases on close (and on unmount) via
  onOpenChange.
• Hover behavior is unchanged when no menu is open; once the menu closes, the peek
  collapses on the next directional exit as before.

Before / after

video.mp4

How did you test this?

• New unit test sidebarPeekStore.test.ts (4 cases: hold blocks endSidebarPeek,
  release restores it, hold cancels a pending hide, cancelSidebarPeek clears the
  hold). pnpm --filter @posthog/ui test passes.
• pnpm --filter @posthog/ui typecheck and Biome pass.
• Manually in the dev app: peek the collapsed sidebar, open the ProjectSwitcher, move
  the cursor into the content and onto the submenus (stays open); close the menu, then
  move the cursor out (collapses normally).

---

[trunk-io]

✨ Submitted to Merge by @tatoalo. It will be added to the merge queue once all branch protection rules pass, there are no merge conflicts with the target branch, and impacted targets for the current PR head commit have been uploaded. See more details here.

[tatoalo]

Thanks!

@aleexzxzxzx could you sign your commits? we are enforcing signed commits, sorry we should make that clearer 🫠