fix(bmm): remove stale 'drafted' story state from docs and workflows

The `drafted` story state is no longer used since create-story now sets
status directly to `ready-for-dev`. This PR removes all references to
this legacy state from BMM documentation and workflow files.

Changes:
- Remove `drafted` from story status definitions and state machine docs
- Remove dead story-context file detection (story-context files no longer exist)
- Replace "draft" verb with "create" in story-related messaging
- Add legacy `drafted` → `ready-for-dev` migration in sprint-status
- Clarify that validate-create-story is optional and doesn't change status
- Document story handoff sequence: create-story → (optional) validate → dev-story

Story lifecycle is now: backlog → ready-for-dev → in-progress → review → done

Closes #1089

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/modules/bmm/docs/quick-start.md

@@ -200,12 +200,12 @@ Once planning and architecture are complete, you'll move to Phase 4. **Important
 3. Tell the agent: "Run sprint-planning"
 4. This creates your `sprint-status.yaml` file that tracks all epics and stories
 
-#### 3.2 Draft Your First Story
+#### 3.2 Create Your First Story
 
 1. **Start a new chat** with the **SM agent**
 2. Wait for the menu
 3. Tell the agent: "Run create-story"
-4. This drafts the story file from the epic
+4. This creates the story file from the epic
 
 #### 3.3 Implement the Story