fix(mysql): preserve table editor alter semantics

[openai0229]

Summary

• infer primary-key ALTER operations from the original editor column flags when no explicit index edit is present
• normalize metadata dimensions by MySQL type so editing existing integer, text, decimal, and temporal columns produces valid DDL
• extend the real MySQL Web product test with a composite primary-key alteration

Verification

• cargo fmt --all -- --check
• cargo test -p chat2db-web
• cargo clippy -p chat2db-web --all-targets --all-features --locked -- -D warnings
• cargo test -p chat2db-web --test native_mysql_editable_ddl_docker -- --ignored

Follow-up to #5.