General: Add Fastlane metadata length validation to CI

[d4rken]

What changed

Added a CI check that validates Fastlane metadata character limits across all locales on every pull request. Catches oversized titles, short descriptions, full descriptions, and changelogs before they reach the Play Store.

Technical Context

• Adapted from the same validation added to SD Maid SE (General: Add Fastlane metadata length validation to CI sdmaid-se#2320)
• Limits: title 30 chars, short_description 80 chars, full_description 3800 hard / 3700 warn, changelogs 500 chars
• Lightweight CI job — no JDK/Gradle setup needed, just checkout + bash
• Forces LC_ALL=C.UTF-8 for consistent multibyte character counting
• All 77 locales currently pass without violations