fix(ui): keep image annotation save action visible

[katya4oyu]

Problem

On narrow screens, the image annotation toolbar extends beyond the visible area, making the Save button unreachable.

Change

• Limit the toolbar to the visible viewport width, including mobile safe areas.
• Keep the existing controls through Clear in one row and make them horizontally scrollable when they do not fit.
• Keep the separator and Save button fixed at the right edge.
• Preserve the existing control order, colors, sizes, and content-sized layout on wider screens.

Verification

• bun test packages/ui/components/ImageAnnotator
• DOM_TESTS=1 bun test --isolate packages/ui/components/ImageAnnotator/ImageAnnotator.layout.test.tsx packages/ui/components/ImageAnnotator/ImageAnnotator.shortcuts.test.tsx
• bun run --cwd packages/ui typecheck
• bun test packages/ui (784 pass, 574 DOM-gated skips, 0 fail)
• bun run build:review
• bun run build:hook
• git diff --check
• Verified on physical Mobile Safari that the toolbar is not clipped and Save remains usable.