Add Docker image facts and Phase 1 scaffold decisions documentation

.claude/agent-memory/directus-devops-architect/reference_timescaledb_ha.md

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+---
+name: TimescaleDB-HA Docker image facts
+description: Key facts about timescale/timescaledb-ha needed for compose and CI configuration
+type: reference
+---
+
+# TimescaleDB-HA Docker image facts
+
+- **Image used**: `timescale/timescaledb-ha:pg16-latest`
+- **PostGIS**: Included by default in all (non-oss) tags. The `-oss` suffix variants ship only OSS-licensed extensions (PostGIS is Apache-licensed, included even in `-oss`). The GitHub README confirms: "By default, the Docker image contains many extensions, including TimescaleDB and PostGIS."
+- **`-all` suffix meaning**: Contains multiple Postgres major versions in one image (e.g. pg13+pg14+pg15). NOT about extra extensions. Not needed for TRM.
+- **PGDATA directory**: `/pgdata` — set via `PGDATA=/pgdata` env var. NOT the standard `/var/lib/postgresql/data`. Volume mounts must target `/pgdata`.
+- **Environment variables**: `POSTGRES_USER`, `POSTGRES_PASSWORD`, `POSTGRES_DB` (same as official postgres image).
+- **Healthcheck**: `pg_isready -U $$POSTGRES_USER -d $$POSTGRES_DB` (double-$ in compose YAML to escape interpolation; the container sees single $ at runtime).
+- **Compatible with `CREATE EXTENSION postgis`**: Yes, binaries present.
+- **Compatible with `CREATE EXTENSION timescaledb`**: Yes, it's the whole point of the image.