fix: align Go-plugin :report JSON keys with bash-strip convention

Every Go-implemented plugin's `:report --format json` now emits keys without the redundant `<plugin>-` head segment, matching the shape bash plugins have always emitted. The CLI flag names and `:set` semantics are unchanged. For backwards compatibility during the 0.38.x patch series, the legacy `<plugin>-<property>` keys are emitted side-by-side with the new keys, and a future major release will drop the legacy keys. `common.ReportSingleApp` is refactored to accept a `ReportSingleAppInput` struct with a `Validate()` method so the input is checked before any work runs, which also catches the latent `"docker options"` reportType bug at the API boundary.

tests/unit/proxy.bats

@@ -372,3 +372,21 @@ teardown() {
     assert_not_external_port $(<$CID_FILE)
   done
 }
+
+@test "(proxy:report) emits new stripped JSON keys alongside legacy" {
+  run /bin/bash -c "dokku proxy:report $TEST_APP --format json | jq -r 'has(\"type\") and has(\"proxy-type\")'"
+  assert_success
+  assert_output "true"
+
+  run /bin/bash -c "dokku proxy:report $TEST_APP --format json | jq -r 'has(\"global-type\") and has(\"proxy-global-type\")'"
+  assert_success
+  assert_output "true"
+
+  run /bin/bash -c "dokku proxy:report $TEST_APP --format json | jq -r 'has(\"computed-type\") and has(\"proxy-computed-type\")'"
+  assert_success
+  assert_output "true"
+
+  run /bin/bash -c "dokku proxy:report $TEST_APP --format json | jq -r 'has(\"enabled\") and has(\"proxy-enabled\")'"
+  assert_success
+  assert_output "true"
+}