test(server): isolate config tests from ambient env via temp-env

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.lock

@@ -1614,6 +1614,7 @@ dependencies = [
  "reqwest",
  "serde_json",
  "sqlx",
+ "temp-env",
  "tokio",
  "tracing",
  "tracing-subscriber",
@@ -1974,6 +1975,15 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "temp-env"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96374855068f47402c3121c6eed88d29cb1de8f3ab27090e273e420bdabcf050"
+dependencies = [
+ "parking_lot",
+]
+
 [[package]]
 name = "thiserror"
 version = "2.0.18"

crates/server/Cargo.toml

@@ -27,3 +27,4 @@ serde_json.workspace = true
 api = { path = "../api" }
 db = { path = "../db" }
 sqlx.workspace = true
+temp-env = "0.3"

crates/server/tests/config.rs

@@ -1,17 +1,27 @@
 use clap::Parser;
 use server::Config;
 
+const CLEARED: [(&str, Option<&str>); 3] = [
+    ("DATABASE_URL", None),
+    ("BIND_ADDR", None),
+    ("APP_NAME", None),
+];
+
 #[test]
 fn parses_from_args_with_defaults() {
+    temp_env::with_vars(CLEARED, || {
         let cfg = Config::try_parse_from(["server", "--database-url", "postgres://localhost/test"])
             .expect("should parse");
 
         assert_eq!(cfg.database_url, "postgres://localhost/test");
         assert_eq!(cfg.bind_addr, "0.0.0.0:8080");
         assert_eq!(cfg.app_name, "Collection Management System");
+    });
 }
 
 #[test]
 fn database_url_is_required() {
+    temp_env::with_vars(CLEARED, || {
         assert!(Config::try_parse_from(["server"]).is_err());
+    });
 }