refactor(schema): consolidate schema definition to single source of truth

Makefile

@@ -0,0 +1,13 @@
+.PHONY: all build generate-schema
+
+all: build
+
+build:
+	go build -o codexis .
+
+generate-schema:
+	@sed 's/^/-- /' db/schema.sql > extension/schema.sql
+	@echo "Generated extension/schema.sql"
+
+clean:
+	rm -f codexis extension/schema.sql