refactor: Use parser-backed annotation discovery across JuLC

[satran004]

Summary

This PR replaces raw substring/regex-based source annotation detection with parser-backed Java AST inspection.

Key changes:

• Adds JavaSourceIntrospector as the shared parser-based source classification utility.
• Migrates Gradle, CLI, testkit, blueprint, playground, and compiler discovery paths to AST-backed annotation checks.
• Fixes false positives where annotations mentioned in comments/Javadocs were treated as real annotations.
• Adds consistent role-conflict detection for classes combining validator annotations with @OnchainLibrary.
• Removes deprecated @Validator and @MintingPolicy annotations and migrates tests/docs/examples to current annotations.
• Improves Gradle plugin generated resource wiring so bundled JuLC sources are produced in a task-owned generated resources directory and consumed through sourceSets.main.resources.

Why

The previous discovery logic used checks like source.contains("@OnchainLibrary") or regex matching. That caused false positives when annotation names appeared in comments or Javadocs, including cases where normal validator files were misclassified as nested on-chain libraries.

Parser-backed discovery keeps source classification aligned with the compiler’s actual view of Java annotations and avoids silent drift across Gradle, CLI, testkit, and playground paths.