chore(fastlane): scaffold F-Droid / Play Store metadata

[Xitee1]

Summary

• Lays down the standard fastlane/metadata/android/<locale>/ tree for en-US and de-DE so F-Droid (and Play Store tooling like Triple-T) can pick up listings from the repo.
• Includes title.txt, short_description.txt, full_description.txt and changelogs/100010.txt per locale.
• Adds the rendered 512x512 store icon at en-US/images/icon.png and copies of the existing docs/screenshots/ PNGs under en-US/images/phoneScreenshots/.
• de-DE deliberately ships text only — F-Droid falls back to en-US images when a locale has none, so we avoid byte duplication until German screenshots actually exist.

Notes for review

• All text files are first-pass drafts derived from the README/strings; please check tone and shorten anything that bumps a limit (title 50, short 80, changelog 500 chars).
• The changelog file is named 100010.txt to match the current versionCode (1.0.1 per the major*100000 + minor*1000 + patch*10 schema).
• No build wiring (no Triple-T plugin) is added; this PR only stores assets in the conventional layout.

Test plan

• find fastlane -type f shows the expected tree.
• Spot-check that short_description.txt lines stay <= 80 characters once finalized.
• When ready, submit the F-Droid metadata PR referencing this layout.

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