chore(deploy): pin dictionary seed to v1.3.0

Bump DICT_VERSION v1.2.1 -> v1.3.0 across the seed surface: .env.example, the
compose build-arg default, both backend Dockerfile stages, the loadtest
Dockerfile, the CI dawg-download version, and the deploy/backend docs.

v1.3.0 drops the abbreviation class from the Russian word list (scrabble-dictionary
#6). This only seeds a FRESH volume; a live contour/prod volume is unaffected (the
.seed_version marker wins — seed-drift guard) and moves to v1.3.0 through the admin
console (ARCHITECTURE §5). Per-contour deploy still overrides via TEST_/PROD_DICT_VERSION.

backend/Dockerfile

@@ -12,7 +12,7 @@
 
 # --- dictionary artifact -----------------------------------------------------
 FROM alpine:3.20 AS dawg
-ARG DICT_VERSION=v1.2.1
+ARG DICT_VERSION=v1.3.0
 RUN apk add --no-cache curl tar
 RUN mkdir -p /dawg \
  && curl -fsSL -o /tmp/dawg.tar.gz \
@@ -42,7 +42,7 @@ FROM gcr.io/distroless/static-debian12:nonroot
 # Re-declare the build arg in this stage so it labels the seed dictionary. One
 # DICT_VERSION drives both the artifact the dawg stage downloads and the version
 # label the binary pins, so the resident version equals the release tag.
-ARG DICT_VERSION=v1.2.1
+ARG DICT_VERSION=v1.3.0
 COPY --from=build /out/backend /usr/local/bin/backend
 # Own the seed dictionary as the nonroot runtime user (UID 65532): a named volume
 # mounted at /opt/dawg inherits this ownership on first use, so the admin console