feat(postgresql): implement automated keyword management system

Implemented a keyword generator that fetches PostgreSQL keywords from the
official kwlist.h file and automatically generates ANTLR grammar rules.

Key features:
- Fetches keywords from PostgreSQL REL_18_STABLE kwlist.h
- Generates parser rules (reserved, unreserved, col_name, type_func_name)
- Inserts lexer keyword rules directly into PostgreSQLLexer.g4
- Handles ANTLR reserved name conflicts (e.g., SKIP → SKIP_P)
- Matches PostgreSQL's official gram.y structure

Changes:
- Add keyword-generator/ tool (Go program)
- Add PostgreSQLKeywords.g4 (auto-generated parser rules)
- Update PostgreSQLLexer.g4 with auto-generated keyword section
- Update PostgreSQLParser.g4 to use kwlist.h token names
- Update Makefile with generate-keywords target
- Fix token references in postgresql_lexer_base.go

The generator ensures keywords are placed before the Identifier rule in
the lexer for correct matching precedence. Keywords are managed between
marker comments for easy regeneration.

Test results: 190/214 tests passing (88.8%)

🤖 Generated with Claude Code (https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: h3n4l

postgresql/Makefile

@@ -1,7 +1,17 @@
 all: build test
 
-build:
+# Generate keyword definitions from PostgreSQL official source
+generate-keywords:
+	@echo "Generating PostgreSQL keyword definitions from REL_18_STABLE..."
+	cd keyword-generator && go run main.go
+	@echo ""
+
+# Build the parser (depends on keyword generation)
+build: generate-keywords
+	@echo "Building PostgreSQL parser..."
 	antlr -Dlanguage=Go -package postgresql -visitor -o . PostgreSQLLexer.g4 PostgreSQLParser.g4
 
-test: 
-	go test -v -run TestPostgreSQLParser
+test:
+	go test -v -run TestPostgreSQLParser
+
+.PHONY: all build test generate-keywords