[codex-analytics] enable general analytics by default (#17389)

## Summary
- Make GeneralAnalytics stable and enabled by default.
- Update feature tests and app-server lifecycle fixtures for explicit
general_analytics=false.
- Keep app-server integration tests isolated from host managed config so
explicit feature fixtures are deterministic.

## Validation
- cargo test -p codex-features
- cargo test -p codex-app-server general_analytics (matched 0 tests)
- cargo test -p codex-app-server thread_start_
- cargo test -p codex-app-server thread_fork_
- cargo test -p codex-app-server thread_resume_
- cargo test -p codex-app-server
config_read_includes_system_layer_and_overrides

codex-rs/app-server/tests/common/mcp_process.rs

@@ -144,6 +144,11 @@ impl McpProcess {
         cmd.current_dir(codex_home);
         cmd.env("CODEX_HOME", codex_home);
         cmd.env("RUST_LOG", "info");
+        // Keep integration tests isolated from host managed configuration.
+        cmd.env(
+            "CODEX_APP_SERVER_MANAGED_CONFIG_PATH",
+            codex_home.join("managed_config.toml"),
+        );
         cmd.env_remove(CODEX_INTERNAL_ORIGINATOR_OVERRIDE_ENV_VAR);
         cmd.args(args);