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/2026-05-19-api-documentation/.pi-map.index.md

@@ -0,0 +1,26 @@
+# openspec/changes/archive/2026-05-19-api-documentation (index)
+dir: openspec/changes/archive/2026-05-19-api-documentation
+
+## role
+Planning and design documents for a comprehensive API documentation improvement initiative targeting a FastAPI-based application.
+## parent
+index: openspec/changes/archive/.pi-map.index.md
+map: openspec/changes/archive/.pi-map.md
+## children
+- openspec/changes/archive/2026-05-19-api-documentation/.openspec
+  index: openspec/changes/archive/2026-05-19-api-documentation/.openspec/.pi-map.index.md
+  map: openspec/changes/archive/2026-05-19-api-documentation/.openspec/.pi-map.md
+- openspec/changes/archive/2026-05-19-api-documentation/specs
+  index: openspec/changes/archive/2026-05-19-api-documentation/specs/.pi-map.index.md
+  map: openspec/changes/archive/2026-05-19-api-documentation/specs/.pi-map.md
+## files
+- design.md
+- proposal.md
+- tasks.md
+## links
+index: openspec/changes/archive/2026-05-19-api-documentation/.pi-map.index.md
+map: openspec/changes/archive/2026-05-19-api-documentation/.pi-map.md
+## workflows
+-
+## dirty
+-