Add output schema registry and public contract docs

docs/configuration.md

@@ -51,6 +51,9 @@ version: 1
 pipeline:
   modules: [glossary, homophones, glossary, spoken_word, grammar]
 
+output:
+  schema: bare-segments
+
 llm:
   proposal:
     base_url: https://openrouter.ai/api/v1
@@ -96,6 +99,12 @@ diagnostics:
   retention: auto
 ```
 
+`output.schema` supports the built-in output schema registry values:
+- `bare-segments` (default)
+- `audita-v1`
+
+Unknown schema names fail clearly before transcript output is written.
+
 Duration-like fields accept either:
 
 - numeric seconds (for example `120`, `3.5`), or