build(android): add fdroid distribution flavor

fastlane/metadata/android/en-US/changelogs/802.txt

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+Adds an F-Droid build without in-app APK updating and fixes Android version metadata.

fastlane/metadata/android/en-US/full_description.txt

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+5chan is a decentralized imageboard client for the Bitsocial protocol.
+
+It keeps the familiar imageboard layout while letting anyone create and operate their own peer-to-peer communities. Boards are owned and moderated by their operators, and users can open any community directly by address.
+
+The Android app supports browsing boards, posting, replying, media upload workflows, account management, themes, and the same directory-based discovery used by the web client.

fastlane/metadata/android/en-US/short_description.txt

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+Decentralized imageboard client for Bitsocial communities

fastlane/metadata/android/en-US/title.txt

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+5chan