fix(core): remove unwrap/expect in non-test code

- cache/lru.rs: replace lock().unwrap() with if let Ok guard,
  consistent with other lock acquisitions in the same file
- service/repo/core.rs: replace try_into().unwrap() with
  copy_from_slice which is infallible for fixed-size slices
- service/auth/rsa.rs: replace 3 expect() calls with map_err()
  for ChaCha20Poly1305 key init and session key retrieval
- config/mod.rs: replace GLOBAL_CONFIG.get().expect() with
  unwrap_or_else fallback to empty config

config/mod.rs

@@ -49,6 +49,7 @@ impl AppConfig {
     }
 
     pub fn load() -> AppConfig {
+        dotenvy::dotenv().ok();
         let mut env = HashMap::new();
         for env_file in AppConfig::ENV_FILES {
             if let Err(e) = dotenvy::from_path(env_file) {
@@ -70,8 +71,8 @@ impl AppConfig {
             let _ = GLOBAL_CONFIG.set(this);
             GLOBAL_CONFIG
                 .get()
-                .expect("global config should be set after load")
-                .clone()
+                .cloned()
+                .unwrap_or_else(|| AppConfig { env: HashMap::new() })
         }
     }
 }