Expand PostgreSQL CREATE TABLE LIKE imports

[yzxcj797]

Summary

PostgreSQL CREATE TABLE ... (LIKE ...) statements are valid, but the SQL parser used by diagram import does not understand them. This adds a PostgreSQL-specific preprocessing pass before parsing:

• split statements while respecting strings, comments, and dollar-quoted bodies;
• remember the definition body of each preceding CREATE TABLE;
• expand a LIKE <known table> clause into that table's definition text;
• preserve any additional columns declared after the LIKE clause;
• support chained copies (A LIKE B, then C LIKE A);
• preserve quoted and schema-qualified identifiers;
• leave unresolved LIKE sources unchanged rather than guessing a definition.

The expansion runs only for PostgreSQL imports and does not alter source for other databases.

Testing

• npm test — 4/4 tests pass
  • basic LIKE ... INCLUDING ALL
  • extra columns and chained copies
  • quoted identifiers plus semicolons in defaults
  • unresolved source left unchanged
• npm run lint — passes with zero warnings
• npm run build — passes (existing lottie-web eval and large-chunk warnings remain)
• npx prettier --check on the new files and package manifest — passes
• git diff --check — passes

Fixes #471.

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