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/index.ts

@@ -1,4 +1,4 @@
-export { execute, ensureGeminiSkillsInjected } from "./execute.js";
+export { execute } from "./execute.js";
 export { testEnvironment } from "./test.js";
 export { parseGeminiJsonl, isGeminiUnknownSessionError } from "./parse.js";
 import type { AdapterSessionCodec } from "@paperclipai/adapter-utils";