bootstrap: implement automated VM bootstrap mechanism for Phase 3

Add systemd service that automatically bootstraps freshly deployed VMs
with their host-specific NixOS configuration from the flake repository.

Changes:
- hosts/template2/bootstrap.nix: New systemd oneshot service that:
  - Runs after cloud-init completes (ensures hostname is set)
  - Reads hostname from hostnamectl (set by cloud-init from Terraform)
  - Checks network connectivity via HTTPS (curl)
  - Runs nixos-rebuild boot with flake URL
  - Reboots on success, fails gracefully with clear errors on failure

- hosts/template2/configuration.nix: Configure cloud-init datasource
  - Changed from NoCloud to ConfigDrive (used by Proxmox)
  - Allows cloud-init to receive config from Proxmox

- hosts/template2/default.nix: Import bootstrap.nix module

- terraform/vms.tf: Add cloud-init disk to VMs
  - Configure disks.ide.ide2.cloudinit block
  - Removed invalid cloudinit_cdrom_storage parameter
  - Enables Proxmox to inject cloud-init configuration

- TODO.md: Mark Phase 3 as completed

This eliminates the manual nixos-rebuild step from the deployment workflow.
VMs now automatically pull and apply their configuration on first boot.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

terraform/vms.tf

@@ -24,6 +24,7 @@ locals {
 
     # Example Minimal VM using all defaults (uncomment to deploy):
     # "minimal-vm" = {}
+    # "bootstrap-verify-test" = {}
   }
 
   # Compute VM configurations with defaults applied
@@ -86,6 +87,13 @@ resource "proxmox_vm_qemu" "vm" {
         }
       }
     }
+    ide {
+      ide2 {
+        cloudinit {
+          storage = each.value.storage
+        }
+      }
+    }
   }
 
   # Start on boot