Convert Diff Forest to SQL Migration Queries

[stifskere]

Sub-issue of #3

Objective

Generate valid SQL migration queries from diff output.

Tasks

Stage 1: PostgreSQL CREATE TABLE (priority)

• Generate ALTER TABLE statements for added columns, removed columns, and modified constraints.
• Validate generated SQL runs correctly on PostgreSQL.

Stage 2: Full MVP / Other Dialects

• Support MySQL, MariaDB, SQLite dialect-specific syntax.
• Handle other schema elements (indexes, triggers).

Note: No Stage 1 for other dialects; prioritize Stage 1 PostgreSQL generation.