Add output schema registry and public contract docs

internal/core/config/file_config_test.go

@@ -11,6 +11,8 @@ func TestParseFileConfigYAMLValid(t *testing.T) {
 version: 1
 pipeline:
   modules: [glossary, homophones, grammar]
+output:
+  schema: audita-v1
 llm:
   proposal:
     base_url: https://example.test/v1
@@ -58,6 +60,9 @@ diagnostics:
 	if cfg.Pipeline == nil || len(cfg.Pipeline.Modules) != 3 {
 		t.Fatalf("unexpected pipeline modules: %#v", cfg.Pipeline)
 	}
+	if cfg.Output == nil || cfg.Output.Schema == nil || *cfg.Output.Schema != "audita-v1" {
+		t.Fatalf("expected output schema audita-v1, got %#v", cfg.Output)
+	}
 	if cfg.LLM == nil || cfg.LLM.Proposal == nil || cfg.LLM.Validation == nil {
 		t.Fatalf("expected llm proposal+validation blocks")
 	}
@@ -78,13 +83,13 @@ version: 1
 pipeline:
   modules: [grammar]
 output:
-  schema: v1
+  unknown: v1
 `
 	_, err := ParseFileConfigYAML([]byte(raw))
 	if err == nil {
 		t.Fatalf("expected unknown field error")
 	}
-	if !strings.Contains(err.Error(), "field output not found") {
+	if !strings.Contains(err.Error(), "field unknown not found") {
 		t.Fatalf("unexpected error: %v", err)
 	}
 }
@@ -116,6 +121,8 @@ func TestApplyFileConfigParsesAndMergesFields(t *testing.T) {
 version: 1
 pipeline:
   modules: [spoken_word, grammar]
+output:
+  schema: audita-v1
 llm:
   proposal:
     model: provider/new-proposal
@@ -164,6 +171,9 @@ diagnostics:
 	if strings.Join(cfg.Modules, ",") != "spoken_word,grammar" {
 		t.Fatalf("unexpected modules: %#v", cfg.Modules)
 	}
+	if cfg.OutputSchema != "audita-v1" {
+		t.Fatalf("unexpected output schema: %q", cfg.OutputSchema)
+	}
 	if cfg.PrimaryLLM.Model != "provider/new-proposal" {
 		t.Fatalf("unexpected proposal model: %q", cfg.PrimaryLLM.Model)
 	}