feat: add --format json to git:report and nginx:report

Mirrors the JSON output convention already used by scheduler:report, builder:report, network:report, and traefik:report. Both plugins now accept `--format json` to emit a single-line JSON object whose keys are the property names with the plugin prefix stripped. Combining `--format` with an info flag is rejected with an error message that matches the Go-based report helper.

Closes #8499

tests/unit/git_3.bats

@@ -731,3 +731,38 @@ teardown() {
   assert_success
   assert_output "master"
 }
+
+@test "(git:report) --format json" {
+  run /bin/bash -c "dokku git:set $TEST_APP deploy-branch main"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku git:report $TEST_APP --format json | jq -r '.\"deploy-branch\"'"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output "main"
+
+  run /bin/bash -c "dokku git:report $TEST_APP --format json | jq -r '.\"global-deploy-branch\"'"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output "master"
+
+  run /bin/bash -c "dokku git:report $TEST_APP --format json | jq -e ."
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku git:report --format json | jq -e ."
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku git:report $TEST_APP --format json --git-deploy-branch"
+  echo "output: $output"
+  echo "status: $status"
+  assert_failure
+  assert_output_contains "--format flag cannot be specified when specifying an info flag"
+}