fix: MCP proxy resilience — discovery cache, default liveness probes

Adds a per-server tools/list cache in McpRouter (positive + negative TTL)
so a slow or dead upstream only stalls the first discovery call, not every
subsequent client request. Invalidated on upstream add/remove.

Health probes now apply a default liveness spec (tools/list via the real
production path) to any RUNNING instance without an explicit healthCheck,
so synthetic and real failures converge on the same signal.

Includes supporting updates in mcpd-client, discovery, upstream/mcpd,
seeder, and fulldeploy/release scripts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/release.sh

@@ -54,7 +54,7 @@ if command -v dpkg &>/dev/null && ! command -v dnf &>/dev/null; then
   sudo dpkg -i "$DEB_FILE" || sudo apt-get install -f -y
 else
   # RPM filenames use x86_64/aarch64, not amd64/arm64
-  local rpm_arch
+  rpm_arch=""
   case "$NATIVE_ARCH" in amd64) rpm_arch="x86_64" ;; arm64) rpm_arch="aarch64" ;; *) rpm_arch="$NATIVE_ARCH" ;; esac
   RPM_FILE=$(ls dist/mcpctl-*.rpm 2>/dev/null | grep -E "[._]${rpm_arch}[._]" | head -1)
   sudo rpm -U --force "$RPM_FILE"