Add mobile loading skeletons and empty states

[jamunatg2006-sys]

Description

This PR improves the mobile app loading and empty-state experience by adding reusable skeleton/empty-state patterns across screens that previously used abrupt loading transitions, spinner-only loading, or plain text placeholders.

Closes #119

Changes Made

• Added skeleton loading UI for QR generation in the Scan screen
• Added skeleton loading UI for in-app WebView loading
• Added empty-state UI when no card is available to generate a QR
• Added empty-state UI in the card picker bottom sheet when no cards exist
• Added empty-state UI for public DevCard profiles with no shared links
• Removed duplicate loading handling and unused empty-state styles from Links screen
• Fixed small TypeScript/lint blockers related to skeleton typing, navigation imports, hook dependencies, and unused variables

Verification

• corepack pnpm --filter @devcard/mobile exec tsc --noEmit
• corepack pnpm --filter @devcard/mobile exec jest --runInBand
• corepack pnpm --filter @devcard/mobile lint
• git diff --check

Screenshots

Not added, because changes are state-based and verified locally through code checks/tests.

[jamunatg2006-sys]

Hi , the mobile checks pass locally:

• corepack pnpm --filter @devcard/mobile exec tsc --noEmit
• corepack pnpm --filter @devcard/mobile exec jest --runInBand
• corepack pnpm --filter @devcard/mobile lint
• git diff --check

The failing Vercel check appears to be due to deployment authorization, not code changes. Please review when possible.

[Harxhit]

Please join our Discord community from the README section so we can communicate properly and provide valid labels for your contributions, which will help you score points in GSSoC.

[jamunatg2006-sys]

Hi @Harxhit, as of now there are no conflicts in the code. Only the PR approval and merge are pending. Please check it once.

[Harxhit]

Hi @Harxhit, as of now there are no conflicts in the code. Only the PR approval and merge are pending. Please check it once.

Your PR is quite large, so please give us some time to properly review all the changes.

[ShantKhatri]

Hi @jamunatg2006-sys , thanks for the contribution, could you please add small demo video, walking us through the UI and feature on you local, I'm here referencing feature developed by you.

I'm at edge to merge the PR, once will have that. Thanks!