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/archive/2026-05-17-auth-oauth/specs/.pi-map.md

@@ -0,0 +1,18 @@
+# openspec/changes/archive/2026-05-17-auth-oauth/specs
+dir: openspec/changes/archive/2026-05-17-auth-oauth/specs
+
+index: openspec/changes/archive/2026-05-17-auth-oauth/specs/.pi-map.index.md
+
+## role
+Contains archived OpenAPI specification files for an OAuth authentication feature change from May 17, 2026, serving as versioned documentation snapshots in the API specification change tracking system.
+## files
+## arch
+Flat directory structure with dated, feature-named archival folders using a timestamped naming convention (YYYY-MM-DD-{feature}) to preserve immutable specification versions for historical reference and auditability.
+## tags
+-
+## symbols
+-
+## workflows
+-
+## dirty
+-