Add guest-only workspace secrets

Add explicit workspace secrets across the CLI, SDK, and MCP, with create-time secret definitions and per-call secret-to-env mapping for exec, shell open, and service start. Persist only safe secret metadata in workspace records, materialize secret files under /run/pyro-secrets, and redact secret values from exec output, shell reads, service logs, and surfaced errors.

Fix the remaining real-guest shell gap by shipping bundled guest init alongside the guest agent and patching both into guest-backed workspace rootfs images before boot. The new init mounts devpts so PTY shells work on Firecracker guests, while reset continues to recreate the sandbox and re-materialize secrets from stored task-local secret material.

Validation: uv lock; UV_CACHE_DIR=.uv-cache make check; UV_CACHE_DIR=.uv-cache make dist-check; and a real guest-backed Firecracker smoke covering workspace create with secrets, secret-backed exec, shell, service, reset, and delete.

src/pyro_mcp/runtime_bundle/linux-x86_64/guest/pyro-init

@@ -0,0 +1,57 @@
+#!/bin/sh
+set -eu
+
+PATH=/usr/sbin:/usr/bin:/sbin:/bin
+AGENT=/opt/pyro/bin/pyro_guest_agent.py
+
+mount -t proc proc /proc || true
+mount -t sysfs sysfs /sys || true
+mount -t devtmpfs devtmpfs /dev || true
+mkdir -p /dev/pts /run /tmp
+mount -t devpts devpts /dev/pts -o mode=620,ptmxmode=666 || true
+hostname pyro-vm || true
+
+cmdline="$(cat /proc/cmdline 2>/dev/null || true)"
+
+get_arg() {
+    key="$1"
+    for token in $cmdline; do
+        case "$token" in
+            "$key"=*)
+                printf '%s' "${token#*=}"
+                return 0
+                ;;
+        esac
+    done
+    return 1
+}
+
+ip link set lo up || true
+if ip link show eth0 >/dev/null 2>&1; then
+    ip link set eth0 up || true
+    guest_ip="$(get_arg pyro.guest_ip || true)"
+    gateway_ip="$(get_arg pyro.gateway_ip || true)"
+    netmask="$(get_arg pyro.netmask || true)"
+    dns_csv="$(get_arg pyro.dns || true)"
+    if [ -n "$guest_ip" ] && [ -n "$netmask" ]; then
+        ip addr add "$guest_ip/$netmask" dev eth0 || true
+    fi
+    if [ -n "$gateway_ip" ]; then
+        ip route add default via "$gateway_ip" dev eth0 || true
+    fi
+    if [ -n "$dns_csv" ]; then
+        : > /etc/resolv.conf
+        old_ifs="$IFS"
+        IFS=,
+        for dns in $dns_csv; do
+            printf 'nameserver %s\n' "$dns" >> /etc/resolv.conf
+        done
+        IFS="$old_ifs"
+    fi
+fi
+
+if [ -f "$AGENT" ]; then
+    python3 "$AGENT" &
+fi
+
+exec /bin/sh -lc 'trap : TERM INT; while true; do sleep 3600; done'