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-server/Cargo.toml

@@ -52,8 +52,13 @@ rustls = { version = "0.23", features = ["ring"] }
 image = { version = "0.25", features = ["png", "jpeg"] }
 sha2 = "0.10"
 mockall = "0.14.0"
+testcontainers = { version = "0.25.0", optional = true }
 # validator = { version = "0.16", features = ["derive"] }
 
+[features]
+default = []
+postgres-tests = ["dep:testcontainers"]
+
 [dev-dependencies]
 tokio = { version = "1", features = ["full"] }
 http = "1"
@@ -63,7 +68,6 @@ bytes = "1"
 anyhow = "1"
 axum-test = "18.1.0"
 pretty_assertions = "1.4.1"
-testcontainers = "0.25.0"
 bon = "3.7.2"
 cookie = "0.18.1"