feat(iac): scaffold orca-platform layout (M1.1)

Lands the per-VM × per-service manifest tree, per-env overlays, VM specs
for SysEleven provisioning, DNS zone placeholder, plan/apply/validate
scripts, and a Makefile.

Structure (per INFRASTRUCTURE.md §2 + IMPLEMENTATION_PLAN.md M1.1):
- manifests/{vm-edge,vm-control,vm-data,stage}/<service>.toml — 35 stubs
- overlays/{dev,stage,prod}/overlay.toml — env-selection rules
- vms/{vm-edge,vm-control,vm-data,stage}.toml — OpenStack flavor/IP/firewall
- dns/yourplatform.com.zone.template — PowerDNS zone (body lands in M0.3)
- cluster.toml.tmpl — cluster-level config rendered per env
- scripts/validate.sh — TOML parse + structural sanity
- scripts/plan.sh — merge manifests + overlay → .orca-out/<env>/
- scripts/apply.sh — push to Orca controller (no-op until M1.2)
- Makefile — validate / plan / apply / diff / clean

Each manifest header names the milestone that finalises its real values;
images today are 'placeholder' for services that need their own repo to
exist first. make validate stays green; apply gates on ORCA_API_URL.

CI workflow swapped from the broken 'orca validate' to 'make validate',
which calls a Python TOML parser plus structural checks (placement.node
matches vm dir, resources.memory present, no mis-nested keys).

Refs: M1.1

manifests/vm-edge/orca-proxy.toml

@@ -0,0 +1,15 @@
+# orca-proxy stub — full config lands in M1.2/M0.3.
+# Host: vm-edge. Resource budget per INFRASTRUCTURE.md §6 co-tenant notes.
+# Wildcard TLS terminator; routing rules land with M0.3.
+
+[[service]]
+name = "orca-proxy"
+image = "orca-managed/orca-proxy:placeholder"
+port = 443
+
+[service.placement]
+node = "vm-edge"
+
+[service.resources]
+memory = "256Mi"
+cpu = 0.5