Implement private messaging system for bot communications

[konard]

🤖 AI-Powered Solution

This pull request implements a private messaging system to address issue #37: "Send bot messages to the user".

📋 Issue Reference

Fixes #37

✨ Solution Overview

The issue requested sending bot messages to users privately instead of posting them as public issue comments, because "bot messages take up too much space". Since GitHub doesn't have a traditional private messaging system, this implementation uses a Bot Communication Repository approach.

🔧 Implementation Details

1. New Interface: IPrivateMessageTrigger<TContext>

• Extends ITrigger<TContext> with private messaging capabilities
• Defines methods for target user, message subject, and content generation
• Backward compatible with existing triggers

2. Enhanced GitHubStorage

• SendPrivateMessage(): Creates issues in a dedicated bot-communications repository
• CreateMinimalIssueComment(): Posts brief notifications with links to private messages
• Automatic user mentions for email notifications

3. Updated IssueTracker

• Automatically detects IPrivateMessageTrigger implementations
• Routes private message triggers through the new messaging system
• Falls back to standard behavior for regular triggers

4. Converted Triggers

• LastCommitActivityTrigger: Now sends activity reports privately
• OrganizationLastMonthActivityTrigger: Sends activity summaries privately

🚀 How It Works

1. Trigger Execution: When a IPrivateMessageTrigger condition is met
2. Private Message Creation: Detailed message is posted to bot-communications repository
3. User Notification: Target user is mentioned (gets email notification)
4. Minimal Comment: Original issue gets a small comment with link to private message
5. Issue Management: Original issue is closed/managed as needed

📊 Benefits

• ✅ Reduced Clutter: Public issue threads stay clean and readable
• ✅ User Notification: Users still get notified via email mentions
• ✅ Message Preservation: All bot messages are preserved in dedicated space
• ✅ Backward Compatibility: Existing triggers continue to work unchanged
• ✅ Flexible Configuration: Bot communication repository name is configurable

📖 Setup Requirements

1. Create a private repository named bot-communications (or configure custom name)
2. Ensure the bot has write access to this repository
3. Deploy the updated bot code

📝 Example Usage

// Before: Creates large public comments
internal class MyTrigger : ITrigger<Issue> 
{
    public async Task Action(Issue issue) 
    {
        await _github.CreateIssueComment(issue.Repository.Id, issue.Number, "Very long report...");
    }
}

// After: Sends private messages
internal class MyTrigger : IPrivateMessageTrigger<Issue> 
{
    public string GetTargetUserLogin(Issue issue) => issue.User.Login;
    public string GetMessageSubject(Issue issue) => "Report Title";
    public async Task<string> GetPrivateMessageContent(Issue issue) => "Very long report...";
    public async Task Action(Issue issue) => await CloseIssue(issue);
}

🧪 Testing

• ✅ Solution compiles successfully
• ✅ Backward compatibility maintained
• ✅ Example documentation provided

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