feat(platform): T01 — standalone PostgreSQL HA chart scaffold

Lays out the S3 platform layer foundation for RAIL-PL-WP-0001 T01:

- .sops.yaml: age encryption policy (shared key, *.sops.yaml pattern)
- .gitignore: prevents accidental commit of decrypted values files
- Makefile: pg-deploy, pg-status, pg-pgpool-check, valkey-deploy,
  valkey-status, backup targets with KUBECONFIG/HELM wiring
- helm/postgresql-ha-values.yaml.template: annotated values schema
  with CHANGEME_ placeholders; includes pgpool-password fix from
  RAIL-BS-WP-0003; notes on single-node vs ThreePhoenix scaling
- docs/postgresql-ha.md: connection strings, DB creation, password
  rotation, pgpool-password critical note, HA failover test ref,
  ThreePhoenix scaling path

To complete T01: fill in CHANGEME_ values, encrypt with sops -e -i,
then run make pg-deploy.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/postgresql-ha.md

@@ -0,0 +1,151 @@
+# PostgreSQL HA — Platform Service
+
+**Chart:** `bitnami/postgresql-ha`
+**Namespace:** `platform`
+**Managed by:** `railiance-platform` (S3)
+**Workplan:** `RAIL-PL-WP-0001`
+
+---
+
+## Architecture
+
+```
+Apps (S5)
+  └── pgpool (load balancer / connection pooler)
+        ├── postgresql-0  [Primary  — repmgr]
+        ├── postgresql-1  [Standby  — repmgr]
+        └── postgresql-2  [Standby  — repmgr]
+```
+
+- **pgpool-II** distributes reads across standbys, routes writes to primary
+- **repmgr** handles automatic failover if the primary disappears
+- All pods in `platform` namespace; app pods connect via pgpool service
+
+## Connection string pattern
+
+```
+postgresql://DBUSER:DBPASS@postgresql-ha-pgpool.platform.svc.cluster.local:5432/DBNAME
+```
+
+Replace `DBUSER`, `DBPASS`, `DBNAME` with the database-specific credentials.
+
+---
+
+## Initial deployment
+
+### Prerequisites
+
+- `railiance-cluster` converged (`make smoke` passes)
+- SOPS age key accessible: `sops -d helm/postgresql-ha-values.sops.yaml` returns plaintext
+- `helm repo add bitnami https://charts.bitnami.com/bitnami && helm repo update` done on the node
+
+### Steps
+
+```bash
+# 1. Ensure the platform namespace exists
+kubectl create namespace platform --dry-run=client -o yaml | kubectl apply -f -
+
+# 2. Deploy (from railiance-platform/)
+make pg-deploy
+
+# 3. Verify
+make pg-status
+# Expected: 3 postgresql pods + 1 pgpool pod, all Running
+
+# 4. Smoke test
+make smoke
+```
+
+---
+
+## Creating a new database for an app
+
+```bash
+# Connect via pgpool
+kubectl exec -it -n platform \
+  $(kubectl get pod -n platform -l app.kubernetes.io/component=pgpool -o name | head -1) \
+  -- psql -U postgres
+
+# Inside psql:
+CREATE DATABASE myapp;
+CREATE USER myapp WITH PASSWORD 'strong-password';
+GRANT ALL PRIVILEGES ON DATABASE myapp TO myapp;
+\c myapp
+GRANT ALL ON SCHEMA public TO myapp;
+\q
+```
+
+Add the user password to the app's own secrets (managed in the app's repo,
+not here). The connection string for the app will be:
+```
+postgresql://myapp:strong-password@postgresql-ha-pgpool.platform.svc.cluster.local:5432/myapp
+```
+
+---
+
+## Password rotation
+
+1. Update the password in the plaintext values template
+2. Re-encrypt: `sops -e -i helm/postgresql-ha-values.sops.yaml`
+3. Upgrade: `make pg-deploy`
+4. Update the app's connection secret to match
+5. Rolling restart the app pods to pick up the new connection
+
+---
+
+## pgpool-password — critical note
+
+The `postgresql.pgpoolPassword` value in the Helm chart maps to the
+`pgpool-password` key in the `postgresql-ha-postgresql` Kubernetes Secret.
+The pgpool container mounts this key at startup; if it is absent, pgpool
+enters CrashLoopBackOff with **no log output**.
+
+**This was the root cause of the 2026-03-10 incident (RAIL-BS-WP-0003).**
+
+Always verify after `helm upgrade`:
+```bash
+kubectl get secret -n platform postgresql-ha-postgresql \
+  -o jsonpath='{.data.pgpool-password}' | base64 -d && echo
+# Must print a non-empty string
+```
+
+---
+
+## HA failover test
+
+Per Decision D3, any change to this service requires a passing failover test:
+
+```bash
+# From railiance-cluster/
+make test-ha-failover GITEA_URL=https://<gitea-hostname>
+```
+
+The test kills the primary PostgreSQL pod and asserts:
+1. repmgr promotes a standby within 60s
+2. All pods return to Running within 120s
+3. pgpool returns to Running (catches the missing-key bug)
+
+---
+
+## Backup
+
+Platform backup (PostgreSQL logical dump) is handled by the `railiance-backup`
+tool in this repo:
+
+```bash
+make backup
+```
+
+This produces an age-encrypted dump uploaded to Nextcloud. For cluster-level
+backup (etcd, kubeconfig), see `railiance-cluster/`.
+
+---
+
+## Scaling to 3 nodes (ThreePhoenix)
+
+When Railiance02 and Railiance03 join the cluster:
+
+1. Switch StorageClass from `local-path` to `longhorn` in the values file
+2. Change `postgresql.podAntiAffinityPreset` from `soft` to `hard`
+3. Run `make pg-deploy` — Helm rolling update spreads pods across nodes
+4. Run `make test-ha-failover` to confirm HA is genuine (not just replicated on one node)