feat(go-services): inventory-go Phase A — read-side scaffold + simple endpoints

First slice of the inventory-service port, running in parallel READ-ONLY against
the production inventory_db (never written):
- main.go/store.go: pgx pool (forced read-only), enum-DB loader extracting
  AttributeSetInfo for set-name resolution, /health, /sets/list, /characters/list.
- Dockerfile + compose service inventory-go (127.0.0.1:8772, enum JSON mounted).

Validated vs the Python service on the same DB: /characters/list 167 chars exact
counts; /sets/list 76 sets EXACT match (ids, names, counts).

Remaining (large): /search/items (40+ filters + enrich_db_item), inventory
fetch, item-processing ingestion (extract_item_properties), and the suitbuilder
solver.

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

go-services/inventory-go/Dockerfile

@@ -0,0 +1,12 @@
+FROM golang:1.25-bookworm AS build
+WORKDIR /src
+COPY . .
+RUN go mod tidy
+ARG BUILD_VERSION=dev
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -trimpath -ldflags "-s -w -X main.buildVersion=${BUILD_VERSION}" -o /out/inventory-go .
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=build /out/inventory-go /inventory-go
+EXPOSE 8772
+ENTRYPOINT ["/inventory-go"]