Replace universal fat APK build with architecture-specific APKs for arm64-v8a, armeabi-v7a, x86, and x86_64. GitHub Actions now builds all variants in parallel using a matrix strategy with separate ccache keys and version codes (multiplied by 100 instead of 10 to allow updates over previously installed universal APKs).
Refactor DNS resolver to implement a multi-provider DoH fallback chain (Cloudflare, Google) with shared connection helpers, proper error handling, and debug-level logging for expected DNS failures. Extract common TXT record parsing and random padding generation into reusable helper methods.
Add validation scripts to ensure build workflow consistency and DNS resolver fallback correctness.
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