fix: remove visual glitches in ModalGallery, placeholder color, borders

[MartinCupela]

🎯 Goal

CLOSES: REACT-863
CLOSES: REACT-859
CLOSES: REACT-854
CLOSES: REACT-864
CLOSES: REACT-874

• [REACT-863: Fix menu and menu item border-radius math (13px vs 8px)](https://linear.app/stream/issue/REACT-863/fix-menu-and-menu-item-border-radius-math-13px-vs-8px)
• [REACT-859: Message input placeholder text color (grey vs blueish design)](https://linear.app/stream/issue/REACT-859/message-input-placeholder-text-color-grey-vs-blueish-design)
• [REACT-854: Consider explicit limit on initial channels query to hide load more](https://linear.app/stream/issue/REACT-854/consider-explicit-limit-on-initial-channels-query-to-hide-load-more)
• [REACT-864: Scroll to bottom button has double border](https://linear.app/stream/issue/REACT-864/scroll-to-bottom-button-has-double-border)
• [REACT-874: Focus ring contrast and scroll in message attachment gallery](https://linear.app/stream/issue/REACT-874/focus-ring-contrast-and-scroll-in-message-attachment-gallery)

Changed the sidebar icons in the demo app according to a new design:
https://www.figma.com/design/Us73erK1xFNcB5EH3hyq6Y/Chat-SDK-Design-System?node-id=10793-508271&m=dev

[github-actions]

Size Change: +57 B (+0.01%)

Total Size: 679 kB

📦 View Changed

Filename	Size	Change
dist/cjs/index.js	270 kB	+7 B (0%)
dist/css/index.css	39.7 kB	+50 B (+0.13%)

ℹ️ View Unchanged

Filename	Size
dist/cjs/audioProcessing.js	1.32 kB
dist/cjs/emojis.js	3.01 kB
dist/cjs/mp3-encoder.js	1.27 kB
dist/cjs/useNotificationApi.js	45.4 kB
dist/css/emoji-picker.css	178 B
dist/css/emoji-replacement.css	456 B
dist/es/audioProcessing.mjs	1.31 kB
dist/es/emojis.mjs	2.52 kB
dist/es/index.mjs	268 kB
dist/es/mp3-encoder.mjs	756 B
dist/es/useNotificationApi.mjs	45.2 kB

_{compressed-size-action}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.55%. Comparing base (6735fa1) to head (f09577b).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3178      +/-   ##
==========================================
+ Coverage   83.50%   83.55%   +0.04%     
==========================================
  Files         434      434              
  Lines       12949    12949              
  Branches     4170     4170              
==========================================
+ Hits        10813    10819       +6     
+ Misses       2136     2130       -6     

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