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/notification-center/.pi-map.index.md

@@ -0,0 +1,29 @@
+# openspec/changes/notification-center (index)
+dir: openspec/changes/notification-center
+
+## role
+Design and specification package for a full-stack Notification Center feature, containing architectural documents, implementation plans, and progress tracking across 4 stacked PRs.
+## parent
+index: openspec/changes/.pi-map.index.md
+map: openspec/changes/.pi-map.md
+## children
+-
+## files
+- .openspec.yaml
+- apply-pr1.md
+- apply-pr2.md
+- apply-pr3.md
+- apply-pr4.md
+- apply-progress.md
+- design.md
+- explore.md
+- proposal.md
+- spec.md
+- tasks.md
+## links
+index: openspec/changes/notification-center/.pi-map.index.md
+map: openspec/changes/notification-center/.pi-map.md
+## workflows
+-
+## dirty
+-