cli: Remove Rust integration test suite and Nix infrastructure

Delete the compiled-binary integration tests (setup_integration,
config_precedence_integration) and their supporting test harness,
along with the associated Nix flake apps/checks that exposed them.

Remove related context contract documents and cross-references
throughout the codebase.

Author: davidabram

cli/flake.nix

@@ -111,18 +111,6 @@
           };
         };
 
-        apps.config-precedence-integration-tests = {
-          type = "app";
-          program = toString (
-            pkgs.writeShellScript "sce-config-precedence-integration-tests" ''
-              exec ${rustToolchain}/bin/cargo test --manifest-path cli/Cargo.toml --test config_precedence_integration "$@"
-            ''
-          );
-          meta = {
-            description = "Run config-precedence integration tests for the sce CLI crate";
-          };
-        };
-
         checks.cli-setup-command-surface = mkCheck "sce-cli-setup-command-surface-check" ''
           runHook preCheck
 
@@ -134,15 +122,6 @@
           runHook postCheck
         '';
 
-        checks.cli-setup-integration = mkCheck "sce-cli-setup-integration-check" ''
-          runHook preCheck
-
-          export PATH="${pkgs.git}/bin:$PATH"
-          cargo test --test setup_integration
-
-          runHook postCheck
-        '';
-
         checks.cli-clippy = mkCheck "sce-cli-clippy-check" ''
           runHook preCheck