fix(adapters/gemini-local): address PR review feedback for skills and formatting

- Isolate skills injection using a temporary directory mapped via
  GEMINI_CLI_HOME, mirroring the claude-local sandbox approach
  instead of polluting the global ~/.gemini/skills directory.
- Update the environment probe to use `--output-format stream-json`
  so the payload matches the downstream parseGeminiJsonl parser.
- Deduplicate `firstNonEmptyLine` helper by extracting it to a
  shared `utils.ts` module.
- Clean up orphaned internal exports and update adapter documentation.

packages/adapters/gemini-local/src/server/utils.ts

@@ -0,0 +1,8 @@
+export function firstNonEmptyLine(text: string): string {
+    return (
+        text
+            .split(/\r?\n/)
+            .map((line) => line.trim())
+            .find(Boolean) ?? ""
+    );
+}