feat: add one-click Deploy to Render support

Adds a Render Blueprint (render.yaml) and supporting pieces so nanobot can
be deployed to Render in one click, with persistent memory across deploys.

- render.yaml: web service + 1GB persistent disk mounted at
  /home/nanobot/.nanobot. Prompts for ANTHROPIC_API_KEY and
  NANOBOT_WEB_TOKEN at deploy time (sync: false).
- render-config.json: committed gateway config that wires secrets via
  ${VAR} placeholders (resolved at runtime). Nothing secret is committed.
- entrypoint.sh: adds a branch gated on RENDER=true that copies the config
  onto the mounted disk, chowns the root-owned mount, and drops to the
  non-root nanobot user via setpriv. Local (non-Render) path is unchanged.
- Dockerfile: COPY render-config.json; USER nanobot -> USER root so the
  entrypoint can chown the freshly-mounted disk before dropping privileges;
  add PYTHONUNBUFFERED/PYTHONFAULTHANDLER for diagnosable crash output.
- README.md: Deploy to Render button + section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

entrypoint.sh

@@ -1,5 +1,28 @@
 #!/bin/sh
 dir="$HOME/.nanobot"
+
+# Render deploy path (see render.yaml + render-config.json). Gated on Render's
+# automatic RENDER=true env var so local Docker/podman usage is unaffected.
+# Copies the committed config template onto the mounted disk (wiring secrets via
+# ${VAR} env vars and keeping runtime data on the persistent disk), chowns the
+# root-owned mount, then drops to the non-root nanobot user. Logs each decision
+# so a failed start is diagnosable in Render's logs.
+if [ "$RENDER" = "true" ]; then
+    echo "[entrypoint] Render deploy — starting as $(id)"
+    mkdir -p "$dir" || echo "[entrypoint] warning: mkdir $dir failed"
+    config="$dir/config.json"
+    cp /app/render-config.json "$config" || echo "[entrypoint] warning: cp config failed"
+    if [ "$(id -u)" = "0" ]; then
+        chown -R nanobot:nanobot "$dir" || echo "[entrypoint] warning: chown $dir failed"
+        if setpriv --reuid=nanobot --regid=nanobot --init-groups true 2>/dev/null; then
+            echo "[entrypoint] dropping privileges to nanobot via setpriv"
+            exec setpriv --reuid=nanobot --regid=nanobot --init-groups nanobot "$@" --config "$config"
+        fi
+        echo "[entrypoint] setpriv privilege-drop not permitted — running as root"
+    fi
+    exec nanobot "$@" --config "$config"
+fi
+
 if [ -d "$dir" ] && [ ! -w "$dir" ]; then
     owner_uid=$(stat -c %u "$dir" 2>/dev/null || stat -f %u "$dir" 2>/dev/null)
     cat >&2 <<EOF