feat(mobile): replace Univer footer with native sheet tabs

- Add native React Native sheet tabs with shadcn/ui styling
- Remove Univer's built-in footer and toolbar in read-only mode
- Tabs use muted background with pill-style active state
- Horizontally scrollable for spreadsheets with many sheets
- Clean up old footer-related CSS and JavaScript hacks
  - Add chevron and check icons to MdiIcon component

Author: typelets

apps/mobile/v1/src/components/MdiIcon.tsx

@@ -7,6 +7,8 @@ export const mdiVectorSquare = 'M2,2H8V4H16V2H22V8H20V16H22V22H16V20H8V22H2V16H4
 export const mdiFileTableBoxOutline = 'M19 3H5C3.89 3 3 3.89 3 5V19C3 20.1 3.9 21 5 21H19C20.1 21 21 20.1 21 19V5C21 3.89 20.1 3 19 3M19 19H5V5H19V19M7 7H11V11H7V7M7 13H11V17H7V13M13 7H17V11H13V7M13 13H17V17H13V13Z';
 export const mdiCodeTags = 'M14.6,16.6L19.2,12L14.6,7.4L16,6L22,12L16,18L14.6,16.6M9.4,16.6L4.8,12L9.4,7.4L8,6L2,12L8,18L9.4,16.6Z';
 export const mdiFileDocumentOutline = 'M6,2A2,2 0 0,0 4,4V20A2,2 0 0,0 6,22H18A2,2 0 0,0 20,20V8L14,2H6M6,4H13V9H18V20H6V4M8,12V14H16V12H8M8,16V18H13V16H8Z';
+export const mdiChevronDown = 'M7.41,8.58L12,13.17L16.59,8.58L18,10L12,16L6,10L7.41,8.58Z';
+export const mdiCheck = 'M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z';
 
 interface MdiIconProps {
   path: string;