fix: use epic-specific tracking files for parallel epic processing

- Change tracking file from `.autonomous-epic-progress.yaml` to
  `.autonomous-epic-progress-epic-{{epic_num}}.yaml`
- Prevents race conditions when multiple epics run in parallel
- Each epic now maintains isolated tracking state
- Updates: README.md, instructions.xml (4 locations), workflow.yaml

Resolves issue where parallel epic processing would stomp on
shared tracking file causing data loss and synchronization issues

src/modules/bmm/workflows/4-implementation/autonomous-epic/README.md

@@ -265,7 +265,10 @@ Next Steps:
 
 ### Progress File
 
-Autonomous epic maintains state in `.autonomous-epic-progress.yaml`:
+Autonomous epic maintains state in `.autonomous-epic-progress-epic-{{epic_num}}.yaml`:
+
+> **Note:** Each epic gets its own tracking file to support parallel epic processing.
+> For example: `.autonomous-epic-progress-epic-02.yaml` for epic 02.
 
 ```yaml
 epic_num: 2

src/modules/bmm/workflows/4-implementation/autonomous-epic/instructions.xml

@@ -184,7 +184,7 @@
       <output>📝 Staying on current branch: {{current_branch}} (parallel epic mode)</output>
     </check>
 
-    <action>Initialize progress tracking file:
+    <action>Initialize progress tracking file at: .autonomous-epic-progress-epic-{{epic_num}}.yaml
       - epic_num
       - started timestamp
       - total_stories
@@ -319,7 +319,7 @@
           </check>
 
           <action>Increment success_count</action>
-          <action>Update progress file</action>
+          <action>Update progress file: .autonomous-epic-progress-epic-{{epic_num}}.yaml</action>
         </try>
 
         <catch>
@@ -332,7 +332,7 @@
       <output>Progress: {{success_count}} ✅ | {{failure_count}} ❌ | {{remaining}} pending</output>
     </loop>
 
-    <action>Update progress file status: complete</action>
+    <action>Update progress file status to complete: .autonomous-epic-progress-epic-{{epic_num}}.yaml</action>
   </step>
 
   <step n="4" goal="Epic completion and reporting">
@@ -382,7 +382,7 @@
       <action>Update sprint-status: epic-{{epic_num}} = "done"</action>
     </check>
 
-    <action>Remove progress file</action>
+    <action>Remove progress file: .autonomous-epic-progress-epic-{{epic_num}}.yaml</action>
   </step>
 
 </workflow>

src/modules/bmm/workflows/4-implementation/autonomous-epic/workflow.yaml

@@ -13,7 +13,7 @@ story_dir: "{implementation_artifacts}"
 # Workflow components
 installed_path: "{project-root}/_bmad/bmm/workflows/4-implementation/autonomous-epic"
 instructions: "{installed_path}/instructions.xml"
-progress_file: "{story_dir}/.autonomous-epic-progress.yaml"
+progress_file: "{story_dir}/.autonomous-epic-progress-epic-{epic_num}.yaml"
 
 # Variables
 epic_num: "" # User provides or auto-discover next epic