fix(docker): bump tzdata Alpine pin from 2026a-r0 to 2026b-r0

Alpine 3.22 main repo rotated tzdata to 2026b-r0, breaking apk add
for existing 2026a-r0 pin. Bump both builder and production stages
to restore CI Docker builds. Fixes blocked Dependabot PRs #79–#83.

Refs #84

Author: nayrosk

Dockerfile

@@ -13,7 +13,7 @@ ARG REVISION=unknown
 # Automated bumps deferred to v0.5.x (Renovate config).
 RUN apk add --no-cache \
         ca-certificates=20260413-r0 \
-        tzdata=2026a-r0
+        tzdata=2026b-r0
 
 WORKDIR /build
 
@@ -54,7 +54,7 @@ LABEL org.opencontainers.image.title="Pebblify" \
 # Automated bumps deferred to v0.5.x (Renovate config).
 RUN apk add --no-cache \
         ca-certificates=20260413-r0 \
-        tzdata=2026a-r0 \
+        tzdata=2026b-r0 \
         wget=1.25.0-r1 \
     && addgroup -g 10000 pebblify \
     && adduser -D -H -u 10000 -G pebblify -s /sbin/nologin pebblify