feat: Add update_issue_comment tool

[PreistlyPython]

Summary

Implements issue #1083 by adding a new update_issue_comment tool to the GitHub MCP server, enabling users to modify existing issue comments programmatically.

Changes Made

• New Tool: update_issue_comment with full parameter validation
• API Integration: Uses GitHub's EditComment API endpoint
• Error Handling: Comprehensive validation and error responses
• Testing: 5 test cases covering success, errors, and edge cases
• Documentation: Auto-generated tool schema snapshots

Implementation Details

Tool Parameters

• comment_id (string, required): Comment's unique identifier
• issue_number (number, required): Target issue number
• owner (string, required): Repository owner
• repo (string, required): Repository name
• body (string, required): New comment content

Features

✅ Parameter Validation: Validates all required parameters with meaningful error messages
✅ ID Parsing: Proper comment ID validation (must be positive integer)
✅ Content Validation: Prevents empty or whitespace-only comments
✅ Error Handling: Handles GitHub API errors (404, permissions, etc.)
✅ Existing Patterns: Follows codebase conventions and patterns

Files Modified

• pkg/github/issues.go: Added UpdateIssueComment function and helper
• pkg/github/issues_test.go: Added comprehensive test suite (5 test cases)
• pkg/github/tools.go: Registered tool in issues toolset
• pkg/github/__toolsnaps__/update_issue_comment.snap: Tool schema validation

Test Results

✅ TestUpdateIssueComment/success - Updates comment successfully
✅ TestUpdateIssueComment/not_found - Handles 404 responses gracefully  
✅ TestUpdateIssueComment/missing_parameters - Validates required parameters
✅ TestUpdateIssueComment/invalid_comment_id - Validates ID format
✅ TestUpdateIssueComment/empty_body - Prevents empty content

Test plan

• Unit tests pass for new functionality
• All existing tests continue to pass (no regressions)
• Tool schema validation via snapshots
• Manual testing with GitHub API responses
• Parameter validation edge cases covered

Fixes #1083

🤖 Generated with Claude Code