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.

plugins/buildpacks/report.go

@@ -34,10 +34,18 @@ func ReportSingleApp(appName string, format string, infoFlag string) error {
 		flagKeys = append(flagKeys, flagKey)
 	}
 
-	trimPrefix := false
-	uppercaseFirstCharacter := true
 	infoFlags := common.CollectReport(appName, infoFlag, flags)
-	return common.ReportSingleApp("buildpacks", appName, infoFlag, infoFlags, flagKeys, format, trimPrefix, uppercaseFirstCharacter)
+	return common.ReportSingleApp(common.ReportSingleAppInput{
+		ReportType:              "buildpacks",
+		AppName:                 appName,
+		InfoFlag:                infoFlag,
+		InfoFlags:               infoFlags,
+		InfoFlagKeys:            flagKeys,
+		Format:                  format,
+		TrimPrefix:              true,
+		UppercaseFirstCharacter: true,
+		EmitLegacyPrefix:        true,
+	})
 }
 
 func reportComputedStack(appName string) string {