Add multi-service deployment stack for TRM platform

Initial pilot stack: redis + tcp-ingestion. Designed to grow as the
platform's other services land (processor, postgres+timescale, directus,
react-spa).

- compose.yaml: services as image: references with env-var-driven tags
  and ports. Redis is internal-only (no host port). TCP port 5027
  exposed for GPS device traffic. Persisted Redis volume.
- .env.example: documents TCP_INGESTION_TAG, INSTANCE_ID, PORT, LOG_LEVEL.
  Compose has defaults so the stack starts with no env config.
- README: Portainer Repository Stack instructions, manual deploy fallback,
  network model, planned-services list, why-separate-repo rationale.
- .gitignore: ignore .env

.env.example

@@ -0,0 +1,31 @@
+# Copy to `.env` for local docker-compose runs, OR enter these values in
+# Portainer's Stack → Environment variables UI.
+#
+# All variables have defaults baked into compose.yaml — this file is the
+# documentation of what's configurable, not a hard requirement.
+
+# ---------------------------------------------------------------------
+# tcp-ingestion
+# ---------------------------------------------------------------------
+
+# Image tag to pull. `main` auto-tracks the latest commit on the main branch.
+# In production, pin to a specific commit SHA for reproducibility.
+#   Example: TCP_INGESTION_TAG=af06973
+TCP_INGESTION_TAG=main
+
+# Instance identifier — must be stable across the lifetime of the process.
+# Phase 2's connection registry depends on this; keep it unique per deployed
+# instance (e.g. `stage-1`, `stage-2`, `prod-eu-1`).
+TCP_INGESTION_INSTANCE_ID=stage-1
+
+# Host port that GPS devices connect to. The container always listens on 5027
+# internally; this maps it to a host port. If multiple stacks run on one host,
+# give each a distinct host port (e.g. 5028, 5029).
+TCP_INGESTION_PORT=5027
+
+# ---------------------------------------------------------------------
+# Shared
+# ---------------------------------------------------------------------
+
+# pino log level: fatal | error | warn | info | debug | trace
+LOG_LEVEL=info