Remove final_output tool and improve scout report handback

final_output removal:
- Remove final_output from tool definitions and dispatch
- Update system prompts to request summaries as regular text
- Remove final_output_called field from StreamingState
- Update auto_continue tests to remove final_output_called parameter
- Remove final_output test from tool_execution_test.rs
- Update planner and flock prompts to not reference final_output
- Keep backwards-compat code in feedback_extraction.rs and task_result.rs

Scout report handback:
- Change from file-based to delimiter-based report extraction
- Scout outputs report between ---SCOUT_REPORT_START/END--- markers
- Research tool extracts content between markers, strips ANSI codes
- Add comprehensive tests for extraction and ANSI stripping

657 tests pass.

crates/g3-ensembles/src/flock.rs

@@ -236,7 +236,7 @@ impl FlockMode {
                - The specific requirements that belong to this module\n\
                - Any dependencies on other modules\n\n\
             4. Return your final partitioning exactly once, prefixed by the marker '{{PARTITION JSON}}' followed by a fenced code block that starts with \"```json\" and ends with \"```\". Place only the JSON array inside the fence.\n\
-            5. Use the final_output tool to provide your partitioning as a JSON array of objects, where each object has:\n\
+            5. The JSON array should contain objects, where each object has:\n\
                - \"module_name\": string\n\
                - \"requirements\": string (the requirements text for this module)\n\
                - \"dependencies\": array of strings (names of other modules this depends on)\n\n\