feat: Packer build orchestration (SAND-WP-0012)

Add vm-packer build mode, profile.vm-packer-build, State Hub progress
notes during long provision, docs/runbook, and build mode tests.

profiles/profile.vm-packer-build.yaml

@@ -0,0 +1,37 @@
+id: profile.vm-packer-build
+version: "1.0.0"
+extension: ext.vm-packer
+isolation:
+  level: microvm
+network:
+  default: deny
+  egress: []
+workspace:
+  mode: remote-canonical
+  access: rw
+scope_default: session
+ttl:
+  default: 12h
+  max: 48h
+  idle_reap: null
+resources:
+  cpu: null
+  memory_mb: null
+setup:
+  instructions: >
+    Trigger a Packer OVA build (the-custodian build-machines conventions).
+    Requires packer and VirtualBox on the placement host. Pass
+    --input packer_template=~/the-custodian/infra/build-machines/haskell
+    and --input vm_name=haskell-build (or vm=haskell-build). Attach mode
+    uses profile.vm-haskell-build instead.
+  secret_refs: []
+placement:
+  prefer: [localhost]
+  fallback: [workstation]
+reachability:
+  tunnel: ops-bridge
+  identity: ops-warden
+metadata:
+  cost_class: self-hosted
+  latency_class: standard
+  observability: none