refactor(web): rely on preview dialog containment

[lyzno1]

Summary

• remove redundant click-propagation handlers from image, audio, video, and PDF preview content
• rely on Dify UI Dialog disablePointerDismissal for pointer containment
• click real preview content in tests and verify dialogs stay open
• remove seven suppressions owned only by those handlers

Review boundary

DOM nodes, classes, media controls, drag, zoom, hotkeys, close behavior, portals, and Dialog configuration are unchanged. Audio and video caption debt and the separate image drag baseline remain out of scope.

Visual regression review

There is no element, class, style, or rendering diff. No new visual state is introduced.

Verification

• four focused suites: 42/42 passed
• standalone a11y lint: 0 new diagnostics
• full static check: 0 errors
• suppression delta: -7
• diff check: passed

Dependency and rollback

Independent root layer; the former PDF icon child is closed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.43%. Comparing base (7522ae1) to head (d93c661).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #40363      +/-   ##
==========================================
- Coverage   86.47%   86.43%   -0.04%     
==========================================
  Files        5264     5107     -157     
  Lines      294867   290736    -4131     
  Branches    59029    57924    -1105     
==========================================
- Hits       254976   251289    -3687     
+ Misses      34950    34506     -444     
  Partials     4941     4941              

Flag	Coverage Δ
cli	?
dify-ui	93.49% <ø> (ø)
web	86.11% <ø> (+<0.01%)	⬆️

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