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.

samples/real_live/project_process_meeting/README.md

@@ -31,6 +31,9 @@ Original input files:
 
 Reference material:
 
+- `meeting_context.yaml`: manually maintained Meeting Context V1 scaffold for
+  reliable metadata. It can be validated and injected into chunk extraction
+  with `--meeting-context`; later pipeline stages are not connected yet.
 - `reference/human_reference_protocol.md`: not currently included. No exact
   existing human-written protocol file was found in the repository workspace.