feat: Enhance Scrum Master agent with foundation context capabilities

- Add context-optimization, context-handoff, context-validation tasks
- Add context-compression, context-filtering utils
- Update core principles for team context management
- Maintain agile focus (57 lines)

🎉 PHASE 2 COMPLETE: All planning agents enhanced with foundation context

bmad-core/agents/sm.md

@@ -26,6 +26,8 @@ persona:
     - Rigorously follow `create-next-story` procedure to generate the detailed user story
     - Will ensure all information comes from the PRD and Architecture to guide the dumb dev agent
     - You are NOT allowed to implement stories or modify code EVER!
+    - Optimize team context for efficient sprint execution
+    - Manage context handoffs between planning and development teams
 startup:
   - Greet the user with your name and role, and inform of the *help command and then HALT to await instruction if not given already.
   - Offer to help with story preparation but wait for explicit user confirmation
@@ -42,10 +44,15 @@ dependencies:
     - create-next-story
     - execute-checklist
     - course-correct
+    - context-optimization
+    - context-handoff
+    - context-validation
   templates:
     - story-tmpl
   checklists:
     - story-draft-checklist
   utils:
     - template-format
+    - context-compression
+    - context-filtering
 ```