chore: track all project map and index files

Add generated .pi-map.md and .pi-map.index.md files across the repository
so the project navigation maps are shared and versioned. These artifacts
are maintained by project_map_init/patch/validate and must be kept in
sync with source edits.

Note: .cache/ remains ignored (added in previous commit).

openspec/changes/backend-frontend-refactoring/.pi-map.index.md

@@ -0,0 +1,23 @@
+# openspec/changes/backend-frontend-refactoring (index)
+dir: openspec/changes/backend-frontend-refactoring
+
+## role
+This package contains planning and specification documents for a pure structural refactoring to decompose monolithic backend/frontend modules into domain-based subpackages while preserving all API contracts and behavior.
+## parent
+index: openspec/changes/.pi-map.index.md
+map: openspec/changes/.pi-map.md
+## children
+-
+## files
+- .openspec.yaml
+- design.md
+- proposal.md
+- spec.md
+- tasks.md
+## links
+index: openspec/changes/backend-frontend-refactoring/.pi-map.index.md
+map: openspec/changes/backend-frontend-refactoring/.pi-map.md
+## workflows
+-
+## dirty
+-