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.

tests/gold/responsibility_attribution_negative/README.md

@@ -7,9 +7,14 @@ The scenario includes a Marketing participant who comments critically on
 Business Development criteria. No one assigns that participant responsibility
 for defining the criteria, and the participant does not accept such a task.
 
-Expected behavior:
+Scope:
 
 - Do not assign Business Development criteria to the Marketing participant.
 - Do not reclassify the Marketing participant as Business Development.
-- Preserve the objection as a position.
 - Keep responsibility open unless explicitly assigned.
+- Preserve the agreed next step to ask Business Development for an owner.
+
+Exclusions:
+
+- This scenario does not test whether the objection is extracted as a position.
+- Position extraction is covered by `position_explicit_objection`.