Implement Meeting Context V1 and extraction improvements

Introduce Meeting Context V1 with YAML schema, validation and template.
Support optional --meeting-context during chunk extraction.
Inject authoritative Meeting Context into extraction prompts.
Record Meeting Context provenance in extraction output.
Activate todos.md in shared prompt assembly.
Strengthen responsibility attribution and decision/todo boundaries.
Add focused Gold scenarios and validation tests.
Update architecture and pipeline documentation.

ROADMAP.md

@@ -193,6 +193,10 @@ Deliverables:
 - FFmpeg integration.
 - Meeting metadata capture.
 - Participant entry.
+- Meeting Context V1 exists as a manually maintained YAML structure with
+  validation, optional extraction prompt integration and extraction provenance;
+  future work should add GUI entry and conservative integration with later
+  pipeline stages.
 - GUI.
 - Stable deployment process.
 - Export workflows.