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).

docs/superpowers/specs/.pi-map.index.md

@@ -0,0 +1,20 @@
+# docs/superpowers/specs (index)
+dir: docs/superpowers/specs
+
+## role
+Contains technical design specifications for planned system features, serving as architectural decision records and implementation blueprints for authentication and session management capabilities.
+## parent
+index: docs/superpowers/.pi-map.index.md
+map: docs/superpowers/.pi-map.md
+## children
+-
+## files
+- 2026-05-17-auth-oauth-design.md
+- 2026-05-24-session-branch-selection-design.md
+## links
+index: docs/superpowers/specs/.pi-map.index.md
+map: docs/superpowers/specs/.pi-map.md
+## workflows
+-
+## dirty
+-