Reduce app-server test timeout pressure (#13884)

## What changed
- The auth/account/fuzzy-file-search test configs disable unrelated
`shell_snapshot` setup.
- The fuzzy-file-search fixture set was reduced so the stop-updates test
does less incidental work before reaching the assertion.

## Why this fixes the flake
- These failures were caused by cumulative timeout pressure, not by a
missing product-level delay.
- The old tests were paying for shell snapshot initialization and extra
fixture volume that were not part of the behavior being validated.
- Removing that incidental work keeps the same coverage but shortens the
critical path enough that the tests finish comfortably inside the
existing timeout budget, which is the right fix versus simply extending
the timeout.

## Scope
- Test-only change.

codex-rs/app-server/tests/suite/auth.rs

@@ -33,6 +33,9 @@ sandbox_mode = "danger-full-access"
 
 model_provider = "mock_provider"
 
+[features]
+shell_snapshot = false
+
 [model_providers.mock_provider]
 name = "Mock provider for test"
 base_url = "http://127.0.0.1:0/v1"
@@ -53,6 +56,9 @@ fn create_config_toml(codex_home: &Path) -> std::io::Result<()> {
 model = "mock-model"
 approval_policy = "never"
 sandbox_mode = "danger-full-access"
+
+[features]
+shell_snapshot = false
 "#,
     )
 }
@@ -65,6 +71,9 @@ model = "mock-model"
 approval_policy = "never"
 sandbox_mode = "danger-full-access"
 forced_login_method = "{forced_method}"
+
+[features]
+shell_snapshot = false
 "#
     );
     std::fs::write(config_toml, contents)