chore: add Docker installation to setup.sh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

setup.sh

@@ -58,6 +58,35 @@ fi
 node --version || error "Node.js install failed"
 npm --version
 
+# ── Docker ─────────────────────────────────────────────────────────────────────
+if command -v docker &>/dev/null; then
+    info "Docker already installed: $(docker --version)"
+else
+    info "Installing Docker..."
+    if command -v apt-get &>/dev/null; then
+        apt-get update -qq
+        apt-get install -y -qq ca-certificates curl gnupg lsb-release
+        install -m 0755 -d /etc/apt/keyrings
+        curl -fsSL https://download.docker.com/linux/$(. /etc/os-release && echo "$ID")/gpg \
+            | gpg --dearmor -o /etc/apt/keyrings/docker.gpg
+        chmod a+r /etc/apt/keyrings/docker.gpg
+        echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] \
+https://download.docker.com/linux/$(. /etc/os-release && echo "$ID") \
+$(. /etc/os-release && echo "$VERSION_CODENAME") stable" \
+            > /etc/apt/sources.list.d/docker.list
+        apt-get update -qq
+        apt-get install -y -qq docker-ce docker-ce-cli containerd.io docker-compose-plugin
+    elif command -v dnf &>/dev/null; then
+        dnf install -y docker docker-compose-plugin
+        systemctl enable --now docker
+    else
+        error "Unsupported package manager — install Docker manually then re-run."
+    fi
+fi
+
+docker --version || error "Docker install failed"
+docker compose version || error "Docker Compose plugin missing"
+
 # ── Project dependencies ───────────────────────────────────────────────────────
 info "Running make install..."
 make install