feat: add support for aichat as AI tool for release notesv0.8.0

- Add --ai-tool flag to release and sync commands
- Support both 'claude' and 'aichat' options (default: claude)
- Update GenerateAIReleaseNotes to handle both tools
- Add tool-specific error messages and hints
- Update documentation with usage examples

This allows users to choose between Claude CLI and aichat for
generating AI-powered release notes.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

1 files changed, 3 insertions, 0 deletions

diff --git a/README.md b/README.md
index 88b6f89..f56554b 100644
--- a/README.md
+++ b/README.md
@@ -172,6 +172,9 @@ gitsyncer release create --update-existing
 
 # Create for specific repository without AI
 gitsyncer release create myproject --no-ai-notes
+
+# Use aichat instead of claude for AI release notes
+gitsyncer release create --ai-tool aichat
 ```
 
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