Migrate remaining logic from StartupFragment to compose and view models

[shobhitagarwal1612]

Towards #1795

This PR aims to shift all non-Android logic, including screen generation, over to Jetpack Compose. This change is a step towards enabling Kotlin Multiplatform (KMP) support (as detailed in issue #3416) by removing the reliance on UI Views for iOS. While the long-term plan is to replace Fragments with Jetpack Navigation Compose, this specific PR focuses solely on the logic migration to Compose. The full switch to Navigation Compose will occur in a single update once every screen has been successfully migrated.

Verified that the functionality doesn't change by running the app locally. Also added test coverage for newly added compose screen and view models.

We've replaced the native progress dialog with a Jetpack Compose version, resulting in a slight visual change. Other screens will be updated to use this new dialog over time for consistency.

@andreia-ferreira @gino-m PTAL?

[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.07%. Comparing base (6a168c3) to head (cf8565b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...groundplatform/android/ui/startup/StartupScreen.kt	63.63%	2 Missing and 2 partials ⚠️
...undplatform/android/ui/components/LoadingDialog.kt	89.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3461      +/-   ##
============================================
+ Coverage     70.02%   70.07%   +0.04%     
- Complexity     1608     1613       +5     
============================================
  Files           320      322       +2     
  Lines          8598     8634      +36     
  Branches        946      951       +5     
============================================
+ Hits           6021     6050      +29     
- Misses         2003     2007       +4     
- Partials        574      577       +3     

Files with missing lines	Coverage Δ
...undplatform/android/ui/startup/StartupViewModel.kt	100.00% <100.00%> (ø)
...n/java/org/groundplatform/android/ui/theme/Size.kt	100.00% <100.00%> (ø)
...undplatform/android/ui/components/LoadingDialog.kt	89.47% <89.47%> (ø)
...groundplatform/android/ui/startup/StartupScreen.kt	63.63% <63.63%> (ø)

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.