Revert "ci(docker): don't fail the image build when the Tailscale package server is down"

This reverts commit 591310b392cc1c5638a3149f3f056c444b92d338.

Dockerfile

@@ -36,27 +36,12 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 # which the user mounts in via docker-compose when they want to enable the
 # Tailscale integration for virtual printers. Without the socket mount, the
 # binary is harmless — the code logs a hint and falls back to self-signed.
-#
-# The Tailscale package server occasionally returns 504; since the CLI is
-# optional (the code falls back to self-signed without it), a fetch failure must
-# not fail the whole image build. Retry a few times for transient blips, and on
-# sustained failure continue building without the CLI (cleaning up the partial
-# apt source so later `apt-get update` layers stay valid) rather than aborting.
-RUN set -eux; \
-    if curl -fsSL --retry 5 --retry-connrefused --retry-delay 3 \
-            https://pkgs.tailscale.com/stable/debian/trixie.noarmor.gpg \
-            -o /usr/share/keyrings/tailscale-archive-keyring.gpg \
-       && curl -fsSL --retry 5 --retry-connrefused --retry-delay 3 \
-            https://pkgs.tailscale.com/stable/debian/trixie.tailscale-keyring.list \
-            -o /etc/apt/sources.list.d/tailscale.list \
-       && apt-get update \
-       && apt-get install -y --no-install-recommends tailscale; then \
-        echo "Tailscale CLI installed."; \
-    else \
-        echo "WARNING: Tailscale package server unavailable; building without the Tailscale CLI (optional integration)."; \
-        rm -f /etc/apt/sources.list.d/tailscale.list /usr/share/keyrings/tailscale-archive-keyring.gpg; \
-    fi; \
-    rm -rf /var/lib/apt/lists/*
+RUN curl -fsSL https://pkgs.tailscale.com/stable/debian/trixie.noarmor.gpg \
+        -o /usr/share/keyrings/tailscale-archive-keyring.gpg \
+    && curl -fsSL https://pkgs.tailscale.com/stable/debian/trixie.tailscale-keyring.list \
+        -o /etc/apt/sources.list.d/tailscale.list \
+    && apt-get update && apt-get install -y --no-install-recommends tailscale \
+    && rm -rf /var/lib/apt/lists/*
 
 # Allow binding to privileged ports (e.g. 990/FTPS) as non-root user.
 # File capabilities are more reliable than Docker cap_add with user: directive,

Dockerfile.test

@@ -49,7 +49,7 @@ HEALTHCHECK NONE
 # -n auto adapts to the host's vCPU count instead of hard-coding 30 —
 # on a 2-vCPU CI / VM runner, -n 30 spawns 30 Python processes fighting
 # for 2 cores, which is mostly IPC + import-thrash overhead.
-CMD ["pytest", "backend/tests/", "--tb=short", "-p", "no:cacheprovider", "-n", "30"]
+CMD ["pytest", "backend/tests/", "--tb=short", "-p", "no:cacheprovider", "-n", "auto"]
 
 # -------------------------------------------
 # Frontend test stage