feat: add Ubuntu 26.04 (Resolute) support

Add Dockerfile, package script, and CI/build configuration for ubuntu-2604 across all build targets.

builder/Dockerfile.ubuntu-2604

@@ -0,0 +1,31 @@
+FROM ubuntu:resolute
+
+ENV OS_IDENTIFIER ubuntu-2604
+
+RUN set -x \
+  && sed -i "s|Types: deb|Types: deb deb-src|g" /etc/apt/sources.list.d/ubuntu.sources \
+  && export DEBIAN_FRONTEND=noninteractive \
+  && apt update \
+  && apt install -y curl libcurl4-openssl-dev libicu-dev libopenblas0-pthread libpcre2-dev libpcre3-dev unzip wget \
+  && apt build-dep -y r-base
+
+# Install s5cmd for S3 uploads (much faster than AWS CLI)
+RUN ARCH=$(uname -m); if [ "$ARCH" = "x86_64" ]; then S5CMD_ARCH="64bit"; else S5CMD_ARCH="arm64"; fi && \
+    curl -sL "https://github.com/peak/s5cmd/releases/download/v2.3.0/s5cmd_2.3.0_Linux-${S5CMD_ARCH}.tar.gz" | tar xz -C /usr/local/bin s5cmd
+
+RUN curl -LO "https://github.com/goreleaser/nfpm/releases/download/v2.18.1/nfpm_$(dpkg --print-architecture).deb" && \
+    apt install -y "./nfpm_$(dpkg --print-architecture).deb" && \
+    rm "nfpm_$(dpkg --print-architecture).deb"
+
+RUN chmod 0777 /opt
+
+# Override the default pager used by R
+ENV PAGER /usr/bin/pager
+
+# R 3.x requires PCRE2 for Pango support on Ubuntu 26
+ENV INCLUDE_PCRE2_IN_R_3 yes
+
+COPY package.ubuntu-2604 /package.sh
+COPY build.sh .
+COPY patches /patches
+ENTRYPOINT ./build.sh