feat: Add Gemini workflows for invoking, reviewing, and triaging issues

- Implemented `gemini-invoke.yml` for invoking Gemini CLI with context from pull requests and issues.
- Created `gemini-review.yml` for automated pull request reviews using Gemini, including structured feedback and suggestions.
- Developed `gemini-scheduled-triage.yml` to automate issue triage on a schedule, identifying unlabeled issues and applying appropriate labels.
- Introduced `gemini-triage.yml` for real-time issue triage based on user input, ensuring correct label application.

.gitignore

@@ -114,3 +114,6 @@ $RECYCLE.BIN/
 *.lnk
 
 # End of https://www.toptal.com/developers/gitignore/api/git,linux,macos,windows,visualstudiocode,dotenv
+
+.gemini/
+gha-creds-*.json