Wire lint detectors into core AAR via lintPublish

[kirich1409]

Without lintPublish, the four lint detectors (#157, #158, #159 + existing HardcodedFlagValue) were published as a separate artifact but never activated automatically in Android Studio — users would have to add featured-lint-rules manually.

Changes

core/build.gradle.kts

• Adds lintPublish(project(":featured-lint-rules")) so the lint JAR is embedded in featured-core.aar
• Sets isTransitive = false on the lintPublish configuration — kotlin-stdlib is provided by the lint host at runtime; without this AGP fails with "Found more than one jar in lintPublish"

sample/android-app/build.gradle.kts

• Adds compileOptions { sourceCompatibility/targetCompatibility = VERSION_21 } to match upstream modules (core, platform, etc. all compile to JVM 21); without this, Kotlin inline functions from JVM-21-compiled deps cause a compile error

Verification

lint.jar embedded in AAR:
  core/build/outputs/aar/core.aar → contains lint.jar ✅

Detector fires on consumer code:
  :sample:android-app:lintRelease →
  Warning: Accessing defaultValue directly on a ConfigParam ... [HardcodedFlagValue] ✅

Closes #— (no issue, discovered during v1.0.0 pre-release verification)

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