Initial monorepo scaffold

Set up top-level structure (backend, frontend, database, infra, shared,
docs) with .gitkeep placeholders, root README, and .gitignore.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -0,0 +1,18 @@
+# Podman
+
+Monorepo for the Podman project.
+
+## Structure
+
+| Directory   | Purpose                                          |
+| ----------- | ------------------------------------------------ |
+| `backend/`  | Server-side application code and APIs            |
+| `frontend/` | Client-side application / UI                     |
+| `database/` | Schema, migrations, and seed data               |
+| `infra/`    | Infrastructure, deployment, and IaC             |
+| `shared/`   | Code shared across packages (types, utils, etc.)|
+| `docs/`     | Project documentation                            |
+
+## Getting started
+
+This is the initial scaffold. Each package will be filled in as development progresses.