feat(adapters/gemini-local): add auth detection, turn-limit handling, sandbox, and approval modes

Incorporate improvements from PR #13 and #105 into the gemini-local adapter:

- Add detectGeminiAuthRequired() for runtime auth failure detection with
  errorCode: "gemini_auth_required" on execution results
- Add isGeminiTurnLimitResult() to detect exit code 53 / turn_limit status
  and clear session to prevent stuck sessions on next heartbeat
- Add describeGeminiFailure() for structured error messages from parsed
  result events including errors array extraction
- Return parsed resultEvent in resultJson instead of raw stdout/stderr
- Add isRetry guard to prevent stale session ID fallback after retry
- Replace boolean yolo with approvalMode string (default/auto_edit/yolo)
  with backwards-compatible config.yolo fallback
- Add sandbox config option (--sandbox / --sandbox=none)
- Add GOOGLE_GENAI_USE_GCA auth detection in environment test
- Consolidate auth detection regex into shared detectGeminiAuthRequired()
- Add gemini-2.0-flash and gemini-2.0-flash-lite model IDs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/adapters/gemini-local/src/index.ts

@@ -7,6 +7,8 @@ export const models = [
   { id: "gemini-2.5-pro", label: "Gemini 2.5 Pro" },
   { id: "gemini-2.5-flash", label: "Gemini 2.5 Flash" },
   { id: "gemini-2.5-flash-lite", label: "Gemini 2.5 Flash Lite" },
+  { id: "gemini-2.0-flash", label: "Gemini 2.0 Flash" },
+  { id: "gemini-2.0-flash-lite", label: "Gemini 2.0 Flash Lite" },
 ];
 
 export const agentConfigurationDoc = `# gemini_local agent configuration
@@ -28,7 +30,8 @@ Core fields:
 - instructionsFilePath (string, optional): absolute path to a markdown instructions file prepended to the run prompt
 - promptTemplate (string, optional): run prompt template
 - model (string, optional): Gemini model id. Defaults to auto.
-- yolo (boolean, optional): pass --approval-mode yolo for unattended operation
+- approvalMode (string, optional): "default", "auto_edit", or "yolo" (default: "default")
+- sandbox (boolean, optional): run in sandbox mode (default: false, passes --sandbox=none)
 - command (string, optional): defaults to "gemini"
 - extraArgs (string[], optional): additional CLI args
 - env (object, optional): KEY=VALUE environment variables