feat(go-services): tracker-go Phase 0/1 — /live + /trails read parity

Parallel Go reimplementation of the dereth-tracker read side, deployed
loopback-only (:8770) and reading the dereth TimescaleDB read-only. The live
Python stack is untouched (added via a compose override, not by editing the
tracked docker-compose.yml).

- Phase 0 scaffold: stdlib net/http server (Go 1.22+ method+path routing),
  /health + /api-version, multi-stage distroless Docker build, and
  go-services/docker-compose.go.yml override (loopback :8770).
- Phase 1: pgx v5 pool forced into read-only transactions, a 5s /live + /trails
  cache loop using the exact main.py:837 SQL, and Python-isoformat timestamps
  so output matches FastAPI's jsonable_encoder.
- compare/compare_live.py: parity harness vs the live Python service. Uses the
  server-stamped received_at to prove same-row full-field equality and to make
  the online-set diff boundary-aware.

Verified on live traffic (73 players): identical online set + 23-key schema,
identity/type parity for all, every same-row pair matches on every field, and
diff-row pairs differ only by the ~6s two-cache refresh skew.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go-services/docker-compose.go.yml

@@ -0,0 +1,40 @@
+# Compose OVERRIDE that adds the Go services alongside the live Python stack.
+# It only ADDS containers; it never modifies the tracked docker-compose.yml or
+# any running Python service.
+#
+# Invoke from the repo root so the Compose project name resolves to
+# "mosswartoverlord" (same as the live stack) and the new container joins the
+# existing default network — letting it reach the `db` service by name:
+#
+#   cd /home/erik/MosswartOverlord
+#   export BUILD_VERSION="$(date -u +%Y.%-m.%-d.%H%M)-$(git rev-parse --short HEAD)"
+#   docker compose -f docker-compose.yml -f go-services/docker-compose.go.yml \
+#       build dereth-tracker-go
+#   docker compose -f docker-compose.yml -f go-services/docker-compose.go.yml \
+#       up -d --no-deps dereth-tracker-go
+#
+# --no-deps keeps Compose from touching the already-running `db` (and anything
+# else). The service is loopback-bound (127.0.0.1:8770); external reach is only
+# ever via the host nginx `location /go/` block (added separately).
+services:
+  dereth-tracker-go:
+    build:
+      context: ./go-services/tracker-go
+      args:
+        BUILD_VERSION: ${BUILD_VERSION:-dev}
+    container_name: dereth-tracker-go
+    ports:
+      - "127.0.0.1:8770:8770"
+    environment:
+      PORT: "8770"
+      # Read-only use of the same dereth TimescaleDB the Python tracker writes.
+      DATABASE_URL: "postgresql://postgres:${POSTGRES_PASSWORD}@db:5432/dereth"
+      LOG_LEVEL: "INFO"
+    depends_on:
+      - db
+    restart: unless-stopped
+    logging:
+      driver: "json-file"
+      options:
+        max-size: "10m"
+        max-file: "3"