Fix field default value quoting and add column comment support

[metowolf]

Summary

This PR fixes two critical issues in schema synchronization:

1. Default value quoting: String type fields (varchar, char, text, etc.) now have their default values properly quoted in DDL statements
2. Column comment support: Column comments are now included in schema comparison and synchronization

Changes

Core Improvements

• Add needsQuotedDefault() method to FieldInfo to determine if a field type requires quoted default values
• Fix default value formatting logic in FieldInfo.String() to handle:
  • String types (char, varchar, text, blob, enum, set, json) with quoted defaults
  • Numeric types (int, tinyint, bigint, decimal, etc.) with unquoted defaults
  • Special keywords (CURRENT_TIMESTAMP, NULL) without quotes
• Add ColumnComment field to FieldInfo struct
• Update FieldInfo.Equals() to include column comment comparison
• Query COLUMN_COMMENT from INFORMATION_SCHEMA.COLUMNS
• Escape single quotes in comments properly

Test Coverage

• Add comprehensive test cases for various field types with default values:
  • varchar/char with string defaults
  • text with string defaults
  • int/tinyint with numeric defaults
  • timestamp with CURRENT_TIMESTAMP
• All existing tests pass

Problem Statement

Before this fix:

-- Incorrect: string default value without quotes
ALTER TABLE `users` MODIFY COLUMN `status` varchar(32) NOT NULL DEFAULT queue;
-- This would cause SQL syntax error

After this fix:

-- Correct: string default value properly quoted
ALTER TABLE `users` MODIFY COLUMN `status` varchar(32) NOT NULL DEFAULT 'queue';

Additionally, column comments were completely ignored during schema comparison, causing synchronization to miss comment differences between source and target databases.

Testing

Tested with:

• MySQL 5.7, 8.0
• Various field types with different default value scenarios
• Fields with and without column comments

Related Issues

This fixes the issue where schema sync would generate invalid SQL statements for fields with string default values, and addresses the missing column comment synchronization feature.

🤖 Generated with Claude Code