fix: ESLint errors and Prettier formatting

ESLint errors:
- usePresenceUpdater: remove redundant `const userId` inside handlePageHide
  that shadowed the outer declaration (no-shadow)
- RoomViewHeader: prefix unused encryptedRoom with _ (no-unused-vars)

Prettier: reformat 14 files to match project style

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/components/GifPicker.tsx

@@ -86,7 +86,8 @@ export function GifPicker({ apiKey, onSelect, requestClose }: GifPickerProps) {
         border: '1px solid color-mix(in srgb, var(--lt-accent-orange) 35%, transparent)',
         borderRadius: '4px',
         overflow: 'hidden',
-        boxShadow: '0 4px 24px color-mix(in srgb, var(--lt-accent-orange) 10%, transparent), 0 0 0 1px color-mix(in srgb, var(--lt-accent-orange) 8%, transparent)',
+        boxShadow:
+          '0 4px 24px color-mix(in srgb, var(--lt-accent-orange) 10%, transparent), 0 0 0 1px color-mix(in srgb, var(--lt-accent-orange) 8%, transparent)',
         width: `${PICKER_WIDTH}px`,
       }
     : {