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.

prompts/decisions.md

@@ -58,6 +58,25 @@ If a statement is only a proposal or suggestion, do not extract it.
 If participants discuss something but do not explicitly agree to it, do not
 extract it.
 
+A personal commitment to perform concrete future work is normally an action
+item, not a decision. Do not extract it as a decision unless the group also
+establishes a binding outcome, rule, approval, rejection, deferral, selection,
+process state, or responsibility policy beyond the personal work assignment
+itself.
+
+Do not duplicate the same proposition under decisions and todos.
+
+A single transcript passage may nevertheless contain both:
+
+- a group-level decision, rule, approval, rejection, deferral or process state
+- and a distinct resulting action item
+
+Extract both when they are semantically separate propositions, even if they
+occur in the same sentence or evidence passage.
+
+A concrete personal work commitment without a separate group-level outcome
+belongs only under todos.
+
 If the transcript describes an existing process, rule, template, document, or
 workflow, do not extract it unless the participants explicitly adopt or change it
 in this meeting.