feat: display open with and link picker as dynamic bottom sheet overlay

[Balajitechlabs]

Summary

This PR improves the "Open with" / Link Actions experience by turning the link picker from a full-screen opaque activity into a translucent Material 3 bottom sheet overlay.

Why this change?

Previously, when setting Essentials as the default browser/link handler or using "Open with", clicking a link launched a full-screen opaque activity. This felt a bit jarring because it completely took you out of the app you were using (like WhatsApp, Twitter, or Reddit).

With this update:

• Clicking a link now brings up a clean bottom sheet directly over your current app with a dimmed background.
• It opens at ~60% screen height by default so you don't lose context, and you can easily drag it up to full screen (100%) or swipe down to dismiss.
• Tapping anywhere outside the sheet instantly closes it and leaves you right where you were.

What's Changed

1. Translucent Floating Window:

   • Configured LinkPickerActivity with taskAffinity="", launchMode="singleInstance", and excludeFromRecents="true" so it floats independently over the caller app rather than pulling the main Essentials app to the front.
   • Updated Theme.Essentials.Translucent to have transparent system bars and disabled OS preview flicker.
   • Removed window enter/exit animations so only the bottom sheet animates smoothly.

2. Material 3 Bottom Sheet UI (LinkPickerAdapter.kt):

   • Replaced the full-screen layout with ModalBottomSheet(skipPartiallyExpanded = false).
   • Preserved the segmented tab switcher ("Open with" / "Share with"), app search filter, and long-press pinning.
   • Retained the URL preview card with quick actions: Copy, Clean tracking parameters (strips utm_*, fbclid, igsh, etc.), and Edit link.
   • Removed obsolete fixed bottom spacers in OpenWithFragment & ShareWithFragment.

3. String Validations:

   • Fixed placeholder specifier mismatches across the translation files so python3 scripts/validate_strings.py passes with 0 errors and 0 warnings.

Testing & Verification

• Built debug APK with ./gradlew assembleDebug (compiled successfully).
• Tested opening links from third-party apps — opens as an overlay, scrolls smoothly, and dismisses cleanly without screen flashing.
• Verified python3 scripts/validate_strings.py passes all 74 files with 0 issues.