Added Fdroid flag

[RohitKushvaha01]

Add F-Droid Build Flavor

This PR introduces a new F-Droid-specific build flavor with the following changes:

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Build Instructions:

# F-Droid flavor (target API level 28)
npm run build paid dev fdroid

# Normal flavor (target API level 34)
npm run build paid dev

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Key Differences in F-Droid Flavor:

• Target API level is set to 28, to allow execution as proot libs are not available
• Prebuilt Proot libraries are excluded from the APK when building the F-Droid flavor, in compliance with F-Droid's packaging rules.

[UnschooledGamer]

Looks okay to me!