test: refresh PostgreSQL coverage after aggregate and CTE expansion

Regenerate the PostgreSQL 18.4 correctness inventory and selected CI fixtures
against grammar commit 06058a7, using the existing pinned PostgreSQL/libpg_query
sources. The corpus remains 51,415 oracle-accepted statements; complete-input
AST results increase from 26,243 to 27,014 with no previously complete case lost.

The 771 gains comprise 638 SELECT, 123 EXPLAIN, nine UPDATE and one INSERT.
Another 79 trailing-input results and 42 statement-type mismatches now report
explicit errors because strict CTE/subquery/function parsing rejects syntax
outside the supported subset. These were not previously complete parses.
Refresh the backlog and transition report, and retain 26,159 selected CI cases
according to the existing selection policy.

Compare regenerated inventory rows with the independently replayed corpus,
then run the full compatibility workflow and its selected fixtures. All
51,415 baseline rows match and all 26,159 selected cases pass. The Python
compatibility harness also passes all 87 unit tests. Coverage counts describe
parse status, classification, AST presence and input consumption, not complete
semantic equivalence with PostgreSQL or production workload coverage.

Only correctness fixtures and compatibility documentation are included;
benchmark programs, timing data, reports and their ancillary edits remain
uncommitted as requested.

Author: renecannao