test(server): gate PostgreSQL tests behind postgres-tests feature

Move testcontainers to optional dependency and create feature flag for database integration tests. Tests without the feature use a dummy pool and skip database operations.

pacman/Justfile

@@ -2,6 +2,9 @@ set shell := ["bash", "-c"]
 
 binary_extension := if os() == "windows" { ".exe" } else { "" }
 
+default:
+	just --list
+
 # Run cargo-vcpkg build for SDL2 dependencies
 vcpkg:
 	cargo vcpkg build
@@ -22,7 +25,7 @@ check:
 
 # Run tests with nextest for pacman package
 test:
-    cargo nextest run -p pacman --no-fail-fast
+    cargo nextest run --all --no-fail-fast
 
 # Auto-format code for pacman package
 format: