[codex] Fix new issue autocomplete pointer selection (#6311)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies.
> - Human operators create and edit issues through modal-heavy board UI
workflows.
> - The new-issue dialog embeds markdown editors that render
autocomplete menus through body-level portals.
> - Radix Dialog treats those portal clicks as outside-dialog pointer
events and prevents their default behavior.
> - That prevention made completion items hard or impossible to select
from inside the new-issue dialog.
> - This pull request marks the markdown editor floating autocomplete
menu as allowed dialog-external UI and extends the dialog
outside-pointer handler to preserve those interactions.
> - The benefit is that users can click/tap autocomplete completions
while keeping the existing modal behavior intact.

## What Changed

- Added a stable `data-paperclip-floating-ui` marker and explicit
pointer event handling to the markdown editor mention/autocomplete
portal.
- Updated the new issue dialog outside-pointer guard so editor
autocomplete portals are handled like Radix popover portals.
- Added regression coverage for markdown editor portal markup and new
issue dialog completion selection behavior.

## Verification

- `pnpm exec vitest run ui/src/components/MarkdownEditor.test.tsx
ui/src/components/NewIssueDialog.test.tsx` passed: 2 files, 38 tests.
- Confirmed the branch is rebased onto current `public-gh/master` before
opening this PR.
- Confirmed the diff does not include `pnpm-lock.yaml` or
`.github/workflows` changes.

## Risks

- Low risk. The change is scoped to allowing pointer events from known
body-level UI portals while keeping other outside-dialog pointer events
under Radix Dialog control.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5 coding agent with repository tool use and local
command execution. Exact hosted context window is not surfaced in this
runtime.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

Screenshot note: this is an interaction/event-handling fix with no
visible UI change; verification is covered by the focused regression
tests above.

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/components/NewIssueDialog.test.tsx

@@ -13,6 +13,13 @@ const dialogState = vi.hoisted(() => ({
   closeNewIssue: vi.fn(),
 }));
 
+const dialogContentState = vi.hoisted(() => ({
+  onPointerDownOutside: null as null | ((event: {
+    detail: { originalEvent: { target: EventTarget | null } };
+    preventDefault: () => void;
+  }) => void),
+}));
+
 const companyState = vi.hoisted(() => ({
   companies: [
     {
@@ -186,13 +193,16 @@ vi.mock("@/components/ui/dialog", () => ({
     children,
     showCloseButton: _showCloseButton,
     onEscapeKeyDown: _onEscapeKeyDown,
-    onPointerDownOutside: _onPointerDownOutside,
+    onPointerDownOutside,
     ...props
   }: ComponentProps<"div"> & {
     showCloseButton?: boolean;
     onEscapeKeyDown?: (event: unknown) => void;
     onPointerDownOutside?: (event: unknown) => void;
-  }) => <div {...props}>{children}</div>,
+  }) => {
+    dialogContentState.onPointerDownOutside = onPointerDownOutside as typeof dialogContentState.onPointerDownOutside;
+    return <div {...props}>{children}</div>;
+  },
 }));
 
 vi.mock("@/components/ui/button", () => ({
@@ -285,6 +295,7 @@ describe("NewIssueDialog", () => {
     dialogState.newIssueOpen = true;
     dialogState.newIssueDefaults = {};
     dialogState.closeNewIssue.mockReset();
+    dialogContentState.onPointerDownOutside = null;
     toastState.pushToast.mockReset();
     mockIssuesApi.create.mockReset();
     mockIssuesApi.upsertDocument.mockReset();
@@ -729,6 +740,27 @@ describe("NewIssueDialog", () => {
     act(() => root.unmount());
   });
 
+  it("allows editor autocomplete portal pointer events inside the modal", async () => {
+    const { root } = renderDialog(container);
+    await flush();
+
+    const menu = document.createElement("div");
+    menu.setAttribute("data-paperclip-floating-ui", "");
+    const option = document.createElement("button");
+    menu.appendChild(option);
+    document.body.appendChild(menu);
+    const preventDefault = vi.fn();
+
+    dialogContentState.onPointerDownOutside?.({
+      detail: { originalEvent: { target: option } },
+      preventDefault,
+    });
+
+    expect(preventDefault).toHaveBeenCalledTimes(1);
+
+    act(() => root.unmount());
+  });
+
   it("warns when a sub-issue stops matching the parent workspace", async () => {
     mockProjectsApi.list.mockResolvedValue([
       {