[infra] Migrate Terraform state from local SOPS to PostgreSQL backend

Two-tier state architecture:
- Tier 0 (infra, platform, cnpg, vault, dbaas, external-secrets): local
  state with SOPS encryption in git — unchanged, required for bootstrap.
- Tier 1 (105 app stacks): PostgreSQL backend on CNPG cluster at
  10.0.20.200:5432/terraform_state with native pg_advisory_lock.

Motivation: multi-operator friction (every workstation needed SOPS + age +
git-crypt), bootstrap complexity for new operators, and headless agents/CI
needing the full encryption toolchain just to read state.

Changes:
- terragrunt.hcl: conditional backend (local vs pg) based on tier0 list
- scripts/tg: tier detection, auto-fetch PG creds from Vault for Tier 1,
  skip SOPS and Vault KV locking for Tier 1 stacks
- scripts/state-sync: tier-aware encrypt/decrypt (skips Tier 1)
- scripts/migrate-state-to-pg: one-shot migration script (idempotent)
- stacks/vault/main.tf: pg-terraform-state static role + K8s auth role
  for claude-agent namespace
- stacks/dbaas: terraform_state DB creation + MetalLB LoadBalancer
  service on shared IP 10.0.20.200
- Deleted 107 .tfstate.enc files for migrated Tier 1 stacks
- Cleaned up per-stack tiers.tf (now generated by root terragrunt.hcl)

[ci skip]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

stacks/phpipam/tiers.tf

@@ -1,10 +0,0 @@
-# Generated by Terragrunt. Sig: nIlQXj57tbuaRZEa
-locals {
-  tiers = {
-    core    = "0-core"
-    cluster = "1-cluster"
-    gpu     = "2-gpu"
-    edge    = "3-edge"
-    aux     = "4-aux"
-  }
-}