fix(chat): enhance pointer event handling in chat components

[WTW0313]

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Summary

Fixes inner ticket 3232

Problem: the chat footer spans the full conversation width, so the blank space around the composer intercepted pointer events and blocked interactions with the content underneath.

Fix: make the footer and inner layout pass pointer events through by default, then restore pointer events only on the actual interactive controls, including the chat input, feature bar, suggested-question buttons, and stop-responding button.

Screenshots

Before:

chat-ui-bug.mp4

After:

chat-ui-fixed.mp4

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.29%. Comparing base (81cc43b) to head (0f346af).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #38385      +/-   ##
==========================================
- Coverage   85.29%   85.29%   -0.01%     
==========================================
  Files        4993     4993              
  Lines      263995   263997       +2     
  Branches    50097    50099       +2     
==========================================
+ Hits       225179   225180       +1     
- Misses      34408    34409       +1     
  Partials     4408     4408              

Flag	Coverage Δ
dify-ui	94.93% <ø> (ø)
web	84.86% <100.00%> (-0.01%)	⬇️

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