devcontainer: bake Tailscale static binary into Alpine image

- Add iproute2 to apk dependencies (needed by tailscaled)
- Download latest Tailscale stable release at build time via pkgs.tailscale.com
  and install tailscale + tailscaled to /usr/local/bin
- Write a _ts_start() shell function into /home/researcher/.bashrc that:
  - starts tailscaled in userspace-networking mode (no TUN device, no root)
  - uses a per-user socket at ~/.local/share/tailscale/tailscaled.sock
  - is a no-op if the daemon is already running

Generated with [Devin](https://cli.devin.ai/docs)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.devcontainer/Dockerfile

@@ -39,8 +39,20 @@ RUN apk add --no-cache \
     bzip2-dev \
     # rclone (Google Drive / S3 / etc.)
     rclone \
+    # ip / iproute2 needed by tailscaled
+    iproute2 \
     && :
 
+# ── Tailscale (static binary — userspace networking, no root required) ────────
+RUN TSVER=$(curl -fsSL https://pkgs.tailscale.com/stable/ \
+      | grep -oP 'tailscale_\K[0-9]+\.[0-9]+\.[0-9]+(?=_amd64\.tgz)' \
+      | sort -V | tail -1) \
+    && curl -fsSL "https://pkgs.tailscale.com/stable/tailscale_${TSVER}_amd64.tgz" \
+       | tar -xz -C /tmp/ \
+    && install -m 755 /tmp/tailscale_${TSVER}_amd64/tailscale  /usr/local/bin/tailscale \
+    && install -m 755 /tmp/tailscale_${TSVER}_amd64/tailscaled /usr/local/bin/tailscaled \
+    && rm -rf /tmp/tailscale_${TSVER}_amd64
+
 # ── uv package manager ────────────────────────────────────────────────────────
 RUN pipx install uv && cp /root/.local/bin/uv /usr/local/bin/uv && cp /root/.local/bin/uvx /usr/local/bin/uvx
 
@@ -105,6 +117,27 @@ RUN curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -
 # ── PATH ──────────────────────────────────────────────────────────────────────
 ENV PATH="/home/researcher/.elan/bin:/home/researcher/venv/bin:/home/researcher/.local/bin:${PATH}"
 
+# ── Tailscale userspace auto-start snippet (written as researcher) ────────────
+RUN mkdir -p /home/researcher/.local/share/tailscale && \
+    printf '%s\n' \
+      '# ── Tailscale (userspace, no root required) ─────────────────────────────' \
+      'export TAILSCALE_SOCKET=/home/researcher/.local/share/tailscale/tailscaled.sock' \
+      'alias tailscale="tailscale --socket=$TAILSCALE_SOCKET"' \
+      '_ts_start() {' \
+      '  if ! /usr/local/bin/tailscale --socket=$TAILSCALE_SOCKET status &>/dev/null; then' \
+      '    mkdir -p /home/researcher/.local/share/tailscale' \
+      '    /usr/local/bin/tailscaled \\' \
+      '      --tun=userspace-networking \\' \
+      '      --socket=$TAILSCALE_SOCKET \\' \
+      '      --statedir=/home/researcher/.local/share/tailscale/ \\' \
+      '      --outbound-http-proxy-listen=localhost:1055 \\' \
+      '      &>>/home/researcher/.local/share/tailscale/tailscaled.log &' \
+      '    sleep 2' \
+      '  fi' \
+      '}' \
+      '_ts_start' \
+      >> /home/researcher/.bashrc
+
 # ── rclone S3 gateway init script ─────────────────────────────────────────────
 COPY --chown=researcher:researcher .devcontainer/init-rclone-s3.sh /home/researcher/init-rclone-s3.sh
 RUN chmod +x /home/researcher/init-rclone-s3.sh