fix: restore stack config step in workflow, add README

Restore Stack Config steps were incorrectly removed in the previous
commit — Pulumi.dev.yaml is gitignored so CI cannot access it without
decoding it from the PULUMI_DEV_YAML secret at runtime.

Also adds README.md documenting the project, stack layout, setup
steps, CI/CD secrets, and roadmap.

.gitea/workflows/deploy-proxmox-infra.yaml

@@ -29,6 +29,9 @@ jobs:
         with:
           node-version: '24'
 
+      - name: Restore Stack Config
+        run: echo "${{ secrets.PULUMI_DEV_YAML }}" | base64 -d > proxmox-infra/Pulumi.dev.yaml
+
       - name: Install Dependencies
         run: npm install
         working-directory: proxmox-infra
@@ -56,6 +59,9 @@ jobs:
         with:
           node-version: '24'
 
+      - name: Restore Stack Config
+        run: echo "${{ secrets.PULUMI_DEV_YAML }}" | base64 -d > proxmox-infra/Pulumi.dev.yaml
+
       - name: Install Dependencies
         run: npm install
         working-directory: proxmox-infra