extract remaining 19 modules from platform, complete stack split [ci skip]

Phase 3: all 27 platform modules now run as independent stacks.
Platform reduced to empty shell (outputs only) for backward compat
with 72 app stacks that declare dependency "platform".
Fixed technitium cross-module dashboard reference by copying file.
Woodpecker pipeline applies all 27+1 stacks in parallel via loop.
All applied with zero destroys.

stacks/sealed-secrets/main.tf

@@ -0,0 +1,4 @@
+module "sealed-secrets" {
+  source = "./modules/sealed-secrets"
+  tier   = local.tiers.cluster
+}