fix(Giphy): use fixed height for giphy preview to prevent layout shifts

[oliverlaz]

Summary

• Set a fixed height (--str-chat__gif-height: 200px) on the giphy container during the preview/shuffle state
• Prevents layout jumps when shuffling between portrait and landscape giphies
• Keeps the Shuffle/Send/Cancel action buttons visible without scrolling
• Add fixed dimensions to the giphy image placeholder so the layout is stable when a giphy fails to load
• Removed stale TODO comment that this change resolves

Test plan

• Type /giphy <query> to trigger a giphy preview
• Click Shuffle repeatedly — verify the container height stays stable and action buttons remain visible
• Verify both portrait and landscape giphies render properly within the fixed height via object-fit: contain
• After sending, verify the giphy renders at full dynamic height (no fixed constraint)
• Simulate a giphy image load failure — verify the placeholder has correct dimensions

[github-actions]

Size Change: +33 B (+0.01%)

Total Size: 614 kB

📦 View Changed

Filename	Size	Change
dist/css/index.css	45.5 kB	+33 B (+0.07%)

ℹ️ View Unchanged

Filename	Size
dist/cjs/audioProcessing.js	1.32 kB
dist/cjs/emojis.js	2.96 kB
dist/cjs/index.js	237 kB
dist/cjs/mp3-encoder.js	1.27 kB
dist/cjs/WithAudioPlayback.js	42.7 kB
dist/css/emoji-replacement.css	456 B
dist/es/audioProcessing.mjs	1.31 kB
dist/es/emojis.mjs	2.47 kB
dist/es/index.mjs	235 kB
dist/es/mp3-encoder.mjs	756 B
dist/es/WithAudioPlayback.mjs	42.5 kB

_{compressed-size-action}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.57%. Comparing base (b5cb01f) to head (7b6fd80).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3095   +/-   ##
=======================================
  Coverage   79.57%   79.57%           
=======================================
  Files         426      426           
  Lines       12181    12181           
  Branches     3914     3914           
=======================================
  Hits         9693     9693           
  Misses       2488     2488           

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