Start giving Junie some code-generation guidelines (#1243)

* Start giving Junie some code-generation guidelines

* Remind Junie to use the existing formatting rules

Author: labkey-jeckels

.junie/guidelines/formatting.md

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+### Code Formatting Guidelines
+
+- All code formatting must strictly adhere to the IntelliJ IDEA project settings defined in `.idea/codeStyles/Project.xml`.
+- Read and follow the specific rules configured in that file for all supported languages (Java, JavaScript, TypeScript, CSS, Python, etc.).

.junie/guidelines/java.md

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+### Java Coding Guidelines
+
+#### General
+- Prefer `Stream` API over traditional for-loops for collection processing.
+- Whenever possible, use try-with-resources for automatic resource management.
+- Always ask before adding, removing, or updating a third-party library dependency.
+- Always use org.jetbrains.annotations.NotNull and org.jetbrains.annotations.Nullable for nullability annotations.
+- Be explicit about nullability in public API method signatures.
+
+#### Logging
+- Use Log4J2 for logging.
+- Name the static logger `LOG` and initialize it using `org.labkey.api.util.logging.LogHelper.getLogger()`.
+
+#### Testing
+- For unit tests, create a static `TestCase` inner class extending `Assert` in the same file as production code.
+- Add new `TestCase` classes to the owning module's list in `getUnitTests()`
+- Use JUnit 4 annotations (e.g., @Test) for these inner test classes.