fix: suppress native mobile context menu on text selection

[grubmanItay]

Description

On mobile (iOS Safari, Android Chrome), long-pressing to select text triggers the native context menu (cut/copy/paste) which overlays the annotation toolbar/picker.

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Fix

Two complementary techniques scoped to the annotation <article> container only:

• CSS: -webkit-touch-callout: none — suppresses iOS Safari callout
• JS: contextmenu event listener with preventDefault() in a dedicated useEffect, gated by (pointer: coarse) media query — suppresses Android Chrome and other mobile browsers

Desktop right-click remains unaffected.

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File changed

File	Change
packages/ui/components/Viewer.tsx	Add useEffect for contextmenu suppression + -webkit-touch-callout: none inline style

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Test Plan

Mobile — iOS Safari

• Long-press to select text — native callout (cut/copy/paste) should NOT appear
• Annotation toolbar/picker appears without obstruction
• Text selection handles still work normally
• All annotation modes work (Markup, Comment, Redline, Label)
• Pinpoint mode tap works without context menu

Mobile — Android Chrome

• Long-press to select text — native context menu should NOT appear
• Annotation toolbar/picker appears without obstruction
• Text selection handles still work normally
• All annotation modes work (Markup, Comment, Redline, Label)

Mobile — Other browsers

• Firefox Mobile — same behavior as above
• Samsung Internet — same behavior as above

Desktop — No regressions

• Right-click on content still works normally (context menu appears)
• Text selection + annotation toolbar works as before
• All modes (Markup, Comment, Redline, Label) unaffected