feat(detector): add Docker and Java/Gradle drift detection (v0.1.9)

[yunaremaia]

Summary

• Adds Docker drift detection: Dockerfile FROM image:tag vs README mentions. Handles variant tags ('24' matches '24-slim', '24-alpine') and multi-stage builds.
• Adds Java/Gradle drift detection: build.gradle sourceCompatibility, jvmTarget, JavaVersion.VERSION_* vs README mentions (major-version comparison).
• Both integrate into scan_repo, CLI output, and --json exit code.

Test plan

• 12 new unit tests covering parsing, no-drift, drift detection, and scan integration
• All 51 tests pass
• Version bumped to 0.1.9

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