fix(dropdown-menu): focus the search when opened inside a dialog

[tmccoy14]

What

A searchable DropdownMenu (and so FilterDropdown / RadioDropdown) opened inside a Dialog or Sheet left focus on the menu, not the search box. Typing still searched, but the visible focus and the screen reader announcement pointed at the menu.

Why

DropdownMenuSearch focuses itself on mount. That runs before the menu's focus scope pauses the dialog's focus trap, so the trap pulls focus back into the dialog, and Radix then focuses the menu itself. Outside a dialog there is no trap, so it worked.

DropdownMenuContent now hands focus to the search the first time the menu takes focus after opening. SelectContent already recovers the same way, so SelectSearch was unaffected.

Found while adopting 4.3.0 in Guardian Studio (the project picker in Manage Roles & Permissions).

Changes

• dropdown-menu.tsx: onFocus recovery on first focus per open. The flag resets when the search is hidden again, which covers a reopen during the exit animation, when the content stays mounted.
• New test: opening a searchable menu inside a Dialog focuses the search. It fails without the fix.
• 4.3.1, with a CHANGELOG entry.

Verification

• pnpm format:check, pnpm lint, pnpm test (38 passing), pnpm build.
• In Studio, with this build in place: click-open, keyboard-open and a quick reopen inside the dialog all focus the search. The page-level filter specs (activity logs, evaluation logs) still pass.

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