test: refresh PostgreSQL corpus after policy and foreign grammar expansion

Regenerate the pinned PostgreSQL 18.4 correctness snapshot for 19d77ca,
including per-statement results, deterministic CI fixtures and the detailed
compatibility backlog. Keep the upstream source corpus and extraction policy
unchanged: 51,415 distinct statements with source file/line provenance.

Deep support increases from 48,313 to 49,120 statements (94.0% to 95.5%).
The 807 improvements consist of 760 prior errors, 35 trailing-input results
and 12 statement-type mismatches. No previously deep statement is lost.
The remaining inventory is 1,542 errors, 423 trailing-input results,
278 type mismatches and 52 partial parses.

The refreshed results match every row in the independently reviewed replay,
including statement types, AST presence, completion and unconsumed input.
All 807 newly supported statements also preserve PostgreSQL raw-AST semantics
after SQL reconstruction, excluding source-position fields only. The generated
CI suite now contains 5,615 cases; fewer backlog cases reflect resolved
productions, not removed source statements.

Validation: full pinned-corpus verification and all 5,615 generated CI cases
pass against the refreshed snapshot. The implementation passed 1,483 tests
with 37 external-backend skips, 11 ASan/UBSan tests and 87 compatibility
harness tests. Independent review approved the five foreign-grammar boundary
fixes and the integrated enum/mapping changes. Record completion in the plan.

Benchmark sources, outputs, reports and benchmark-only README/.gitignore edits
remain uncommitted. This snapshot measures correctness coverage rather than
parser performance or complete PostgreSQL grammar parity.

Author: renecannao