Prepare for AGP 10 migration

[eliotcougar]

Summary

Prepare for AGP 10 by replacing legacy Android DSL and private variant APIs while retaining current upstream's AGP 9.4.1, Gradle 9.6.0, Kotlin/Compose compiler 2.4.20 and license plugin 0.9.91. The app stays on AGP 9; release shrinking remains disabled.

The branch includes upstream/master through 53fce9a8f. Dependency versions, version 2.3.8, application source and native-library revisions match that upstream base. The remaining diff is limited to build-system migration.

Changes

• Enable the modern Android DSL and built-in Kotlin. Remove the standalone Kotlin Android plugin and compatibility opt-outs. Supply the version-catalog KGP dependency on the root buildscript classpath so built-in Kotlin stays aligned with the Compose compiler. Retain JVM target 17.
• Replace applicationVariants and private ApkVariantOutputImpl casts with androidComponents.onVariants, public output properties and BuildConfigField. Retain the exact DISTRIBUTION values, ABI filtering and universal APK behavior. Use the modern jniLibs.directories API.
• Retain the regenerated Gradle 9.6 wrapper scripts/JAR and pinned distribution SHA-256. Upstream now selects the same Gradle version; this PR keeps the complete wrapper update and integrity settings.
• Remove the old SDK, R-class, dependency, resource-value and shrinker compatibility switches. BuildConfig and Compose remain explicitly enabled; this does not enable R8 or resource shrinking.
• Replace CI's line-number-dependent sed insertion with an NDK_VERSION job value used for installation, NDK_HOME and both Gradle invocations. Pin the ordinary Gradle default as well:

ndkVersion = providers.gradleProperty("NDK_VERSION").getOrElse("29.0.14206865")

The NDK strips native libraries, so a plain rebuild needs the release NDK to avoid differing native-library bytes. This preserves intentional overrides and implements the compatibility recommendation from #6219; its JDK pin and exact-tag workflow checks remain independent.

Preserved APK contract

Distribution	Filename	Version code
Play Store	v2rayNG_<version>_<abi>.apk	4_000_000 + baseVersionCode
F-Droid	v2rayNG_<version>-fdroid_<abi>.apk	5_000_000 + 100 * baseVersionCode + abiOffset

F-Droid offsets remain universal=0, arm64-v8a=1, armeabi-v7a=2, x86_64=3 and x86=4. Package IDs, default four-ABI plus universal output, explicit ABI_FILTERS behavior and artifact-upload patterns are preserved.

Validation

Validated at merge commit cf329109, based on upstream 53fce9a8f:

• Play Store and F-Droid debug/release assembly plus both unit-test suites: 201 tasks executed, build successful.
• 81 tests per flavor, 162 total, with zero failures, errors or skips.
• All 20 APKs checked for current version 2.3.8, package IDs, filenames, version-code formulas, ABI sets and required geodata. Every requested ABI includes both HEV libraries and libgojni.so, matching the native-stripping outputs.
• Exact generated DISTRIBUTION values verified in all four variants.
• AGP resolves the default and installed toolchain to NDK 29.0.14206865 without an override; no unstripped-library fallback warnings.
• Strict configuration-cache storage passed with JDK 21, Gradle 9.6.0, two workers and in-process Kotlin compilation.
• Official AndroidLibXrayLite v26.9.9 AAR matches upstream gitlink d0c6c4ae and GitHub's release SHA-256; all four JNI ABIs and geodata verified. Existing HEV inputs retained for unchanged gitlink 64cc609f.
• actionlint 1.7.12 passed with the existing ubuntu-26.04 runner-label exception; git diff --check and instruction-file boundary checks passed.

Not run: production signing CI, device runtime checks or independent cross-machine byte-for-byte reproducibility. The local builds reuse the official native release inputs; this PR prepares the build-system migration and aligns NDK selection without claiming complete reproducibility.