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).

apps/api/alembic/.pi-map.index.md

@@ -0,0 +1,25 @@
+# apps/api/alembic (index)
+dir: apps/api/alembic
+
+## role
+Database migration tooling that manages schema versioning and changes for the API's PostgreSQL database using Alembic with async SQLAlchemy.
+## parent
+index: apps/api/.pi-map.index.md
+map: apps/api/.pi-map.md
+## children
+- apps/api/alembic/versions
+  index: apps/api/alembic/versions/.pi-map.index.md
+  map: apps/api/alembic/versions/.pi-map.md
+## files
+- env.py
+- script.py.mako
+## links
+index: apps/api/alembic/.pi-map.index.md
+map: apps/api/alembic/.pi-map.md
+## workflows
+- change alembic behavior
+  read: env.py, script.py.mako
+- explore alembic subdirectories
+  index: apps/api/alembic/versions/.pi-map.index.md
+## dirty
+-