pgdb1: decommission postgresql host

Remove pgdb1 host configuration and postgres service module.
The only consumer (Open WebUI on gunter) has migrated to local PostgreSQL.

Removed:
- hosts/pgdb1/ - host configuration
- services/postgres/ - service module (only used by pgdb1)
- postgres_rules from monitoring rules
- rebuild-all.sh (obsolete script)

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

docs/plans/pgdb1-decommission.md

@@ -0,0 +1,113 @@
+# pgdb1 Decommissioning Plan
+
+## Overview
+
+Decommission the pgdb1 PostgreSQL server. The only consumer was Open WebUI on gunter, which has been migrated to use a local PostgreSQL instance.
+
+## Pre-flight Verification
+
+Before proceeding, verify that gunter is no longer using pgdb1:
+
+1. Check Open WebUI on gunter is configured for local PostgreSQL (not 10.69.13.16)
+2. Optionally: Check pgdb1 for recent connection activity:
+   ```bash
+   ssh pgdb1 'sudo -u postgres psql -c "SELECT * FROM pg_stat_activity WHERE datname IS NOT NULL;"'
+   ```
+
+## Files to Remove
+
+### Host Configuration
+- `hosts/pgdb1/default.nix`
+- `hosts/pgdb1/configuration.nix`
+- `hosts/pgdb1/hardware-configuration.nix`
+- `hosts/pgdb1/` (directory)
+
+### Service Module
+- `services/postgres/postgres.nix`
+- `services/postgres/default.nix`
+- `services/postgres/` (directory)
+
+Note: This service module is only used by pgdb1, so it can be removed entirely.
+
+### Flake Entry
+Remove from `flake.nix` (lines 131-138):
+```nix
+pgdb1 = nixpkgs.lib.nixosSystem {
+  inherit system;
+  specialArgs = {
+    inherit inputs self;
+  };
+  modules = commonModules ++ [
+    ./hosts/pgdb1
+  ];
+};
+```
+
+### Vault AppRole
+Remove from `terraform/vault/approle.tf` (lines 69-73):
+```hcl
+"pgdb1" = {
+  paths = [
+    "secret/data/hosts/pgdb1/*",
+  ]
+}
+```
+
+### Monitoring Rules
+Remove from `services/monitoring/rules.yml` the `postgres_down` alert (lines 359-365):
+```yaml
+- name: postgres_rules
+  rules:
+    - alert: postgres_down
+      expr: node_systemd_unit_state{instance="pgdb1.home.2rjus.net:9100", name="postgresql.service", state="active"} == 0
+      for: 5m
+      labels:
+        severity: critical
+```
+
+### Utility Scripts
+Delete `rebuild-all.sh` entirely (obsolete script).
+
+## Execution Steps
+
+### Phase 1: Verification
+- [ ] Confirm Open WebUI on gunter uses local PostgreSQL
+- [ ] Verify no active connections to pgdb1
+
+### Phase 2: Code Cleanup
+- [ ] Create feature branch: `git checkout -b decommission-pgdb1`
+- [ ] Remove `hosts/pgdb1/` directory
+- [ ] Remove `services/postgres/` directory
+- [ ] Remove pgdb1 entry from `flake.nix`
+- [ ] Remove postgres alert from `services/monitoring/rules.yml`
+- [ ] Delete `rebuild-all.sh` (obsolete)
+- [ ] Run `nix flake check` to verify no broken references
+- [ ] Commit changes
+
+### Phase 3: Terraform Cleanup
+- [ ] Remove pgdb1 from `terraform/vault/approle.tf`
+- [ ] Run `tofu plan` in `terraform/vault/` to preview changes
+- [ ] Run `tofu apply` to remove the AppRole
+- [ ] Commit terraform changes
+
+### Phase 4: Infrastructure Cleanup
+- [ ] Shut down pgdb1 VM in Proxmox
+- [ ] Delete the VM from Proxmox
+- [ ] (Optional) Remove any DNS entries if not auto-generated
+
+### Phase 5: Finalize
+- [ ] Merge feature branch to master
+- [ ] Trigger auto-upgrade on DNS servers (ns1, ns2) to remove DNS entry
+- [ ] Move this plan to `docs/plans/completed/`
+
+## Rollback
+
+If issues arise after decommissioning:
+1. The VM can be recreated from template using the git history
+2. Database data would need to be restored from backup (if any exists)
+
+## Notes
+
+- pgdb1 IP: 10.69.13.16
+- The postgres service allowed connections from gunter (10.69.30.105)
+- No restic backup was configured for this host