Slim down root AGENTS.md, delete java-development skill, and rename core GEMINI.md to AGENTS.md

Author: lqiu96

.agents/skills/java-development/SKILL.md

@@ -32,45 +32,25 @@ Directories starting with `java-` are client libraries for specific Google Cloud
     - **Logging**: [java-logging](java-logging)
     - **Logging Logback**: [java-logging-logback](java-logging-logback)
 
-## 3. Getting Started
-### Prerequisites
-- Java 11+ (build targets Java 8 bytecode compatibility)
-- Maven 3.0+
-- Bazelisk (for integration tests in `sdk-platform-java`)
-
-### Building the Project
-- Build all modules: `mvn install` from root.
-- Recommended for faster builds: `mvn install -T 1C -P quick-build`.
-- Build specific module: Run `mvn` commands within the module directory.
-
-### Code Formatting
-- Check: `mvn fmt:check`
-- Format: `mvn fmt:format`
-- Tip: Run in specific module to save time.
-
-## 4. Testing Strategy
-- **Unit Tests**: `mvn test`.
-- **Integration Tests**: Module specific, may require emulators or live services.
-- **Core Components Testing**: Components should have adequate unit and integration tests to ensure coverage and correctness.
-
-## 5. Style Guide
+## 3. Style Guide
 1. Minimize visibility scopes. Default to most restrictive access level.
 2. Use short names over fully qualified names.
 3. Avoid calling `@ObsoleteApi` or `@Deprecated` methods and classes.
 4. Avoid unnecessary formatting changes to keep diffs clean.
 5. Use `mvn` for everything other than the `test/integration` folder.
 
-## 6. Dependency Management
+## 4. Dependency Management
 - Do not bump external dependency versions unless for CVE or critical bug fix.
 - Avoid introducing new external dependencies if possible. Prefer Java standard library, then opt for existing dependencies.
 
-## 7. Contribution Guidelines
+## 5. Contribution Guidelines
 - **Commits**: Conventional Commits `<type>(<scope>): <description>`.
 - **Pull Requests**: Submitted via PR, require review. Pull latest from main and resolve conflicts.
 - **Testing**: All new logic should be accompanied by tests.
 
-## 8. Specialized Development Guides
+## 6. Specialized Development Guides
 For development on core components, refer to the following guides in `sdk-platform-java`:
 - **GAPIC Generator**: [sdk-platform-java/gapic-generator-java/DEVELOPMENT.md](sdk-platform-java/gapic-generator-java/DEVELOPMENT.md)
 - **GAX**: [sdk-platform-java/gax-java/DEVELOPMENT.md](sdk-platform-java/gax-java/DEVELOPMENT.md)
 - **Hermetic Build**: [sdk-platform-java/hermetic_build/DEVELOPMENT.md](sdk-platform-java/hermetic_build/DEVELOPMENT.md)
+- **Core Specific Instructions**: [sdk-platform-java/AGENTS.md](sdk-platform-java/AGENTS.md)