test: harden touch and cross-browser interaction coverage

[devkyato]

Goal

Extend the existing browser workflow suite so the editor remains dependable across touch devices and multiple browser engines.

Proposed coverage

• Touch dragging, resizing, panning, and connector creation.
• Compact properties-panel behavior at mobile breakpoints.
• Firefox and Chromium smoke coverage in CI where available.
• Text editing, clipboard, and download behavior on Safari documented through a manual checklist.
• Regression cases for pointer cancellation and lost focus.

Acceptance criteria

• Mobile layouts have no horizontal page overflow.
• Touch gestures do not trigger accidental page scrolling.
• Core project and export workflows pass in supported browsers.
• Browser-specific limitations are documented.

[devkyato]

Done.