feat: reaction icons, GIF playback, comment UX polish

[GraysonCAdams]

Summary

• Replace smiley icon with laughing face (SmileyXEyes) and warning icon with custom double exclamation mark for ‼️ reaction
• Close reaction wheel when user taps the main heart icon; negative reactions (👎, ❓) no longer auto-favorite clips
• One-time startup migration removes favorites that were created only via negative reactions
• Fix GIF search previews not animating (IntersectionObserver now re-runs when results change) and defocus search bar on Enter
• Comment input expands from 1 to 3 lines as text wraps; empty lines stripped from comments; Enter submits, Shift+Enter for newlines

Test plan

• Open a reel and long-press the heart to verify the reaction wheel shows a laughing face icon (not a smiley) and double exclamation marks (not a warning triangle)
• Tap the main heart icon while the reaction wheel is open — it should close the wheel
• React with 👎 or ❓ and verify the clip is NOT auto-favorited
• Open the GIF picker in comments and confirm GIF previews animate when visible
• Type a search query in the GIF picker and press Enter — keyboard should dismiss
• Type a multi-line comment and verify the input box grows up to 3 lines
• Submit a comment with blank lines and verify they are stripped