feat: Add granular feature status stages across all skills

Replaces ambiguous 4-status system with 6 clear stages, one per skill:
Planned → Architected → In Progress → In Review → Approved → Deployed

- architecture: sets "Architected" (was "In Progress")
- frontend + backend: explicitly set "In Progress" with checklist items
- qa: sets "In Review" on start, "Approved" on pass (was only "In Review")
- general rules + INDEX.md: updated valid statuses and descriptions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/backend/SKILL.md

@@ -93,6 +93,10 @@ CREATE INDEX idx_tasks_status ON tasks(status);
 ## Checklist
 See [checklist.md](checklist.md) for the full implementation checklist.
 
+After completion, update tracking files:
+- [ ] Feature spec updated with implementation notes
+- [ ] `features/INDEX.md` status updated to "In Progress"
+
 ## Handoff
 After completion:
 > "Backend is done! Next step: Run `/qa` to test this feature against its acceptance criteria."