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/explorations/.pi-map.index.md

@@ -0,0 +1,25 @@
+# openspec/explorations (index)
+dir: openspec/explorations
+
+## role
+Design exploration and technical specification documents for container instance management system features and architectural improvements.
+## parent
+index: openspec/.pi-map.index.md
+map: openspec/.pi-map.md
+## children
+-
+## files
+- config-profile-multi-repo-mounts.md
+- home-path-expansion.md
+- mount-file-level-overlays.md
+- mount-specificity-ordering.md
+- ssh-key-mounting.md
+- streamline-tool-container-definitions.md
+- terminal-responsiveness.md
+## links
+index: openspec/explorations/.pi-map.index.md
+map: openspec/explorations/.pi-map.md
+## workflows
+-
+## dirty
+-