Reuse shared controls in the rich-text toolbar

[Harry19081]

Problem

The rich-text formatting toolbar implements custom heading, list, and link popovers with duplicate styling and document-level click handling. It cannot adapt control density or popup direction for compact composers near the bottom of a panel.

Solution

Replace the custom popovers with the shared Dropdown, DropdownPanel, DropdownItem, Input, and Button primitives. Add explicit mini/small toolbar sizing and configurable dropdown placement, preserve controlled open state and ARIA semantics, and remove the superseded popup CSS and global outside-click listener.

Potential risks

Dropdown focus and portal behavior now follow the shared component rather than the editor's bespoke event handler; consumers with unusual containment may need an explicit popup position. Existing defaults preserve small controls and bottom-start placement. Manual keyboard, theme, and narrow-panel evidence is pending, so this PR remains a draft.

Audit

The configured frontend-ui-audit skill file was unavailable at both documented locations. A direct design-system pass confirmed the custom popover markup is replaced by existing shared controls, semantic roles are retained, portal z-index comes from the dropdown token, and no new arbitrary color values were added.

Verification

• pnpm exec vitest run src/components/RichTextEditor/FloatingToolbar.test.ts src/components/RichTextEditor/index.test.ts — passed (6 tests).
• ESLint on the 5 changed TypeScript/TSX implementation and test files — passed.
• pnpm typecheck — passed.
• git diff --cached --check — passed before commit.
• Manual desktop verification was not run because local UI control was not authorized for this task.