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>

src/db/src/seed/index.ts

@@ -8,7 +8,8 @@ export interface TemplateEnvEntry {
 }
 
 export interface HealthCheckSpec {
-  tool: string;
+  /** When set, probe sends initialize + tools/call (readiness). When omitted, probe sends tools/list only (liveness). */
+  tool?: string;
   arguments?: Record<string, unknown>;
   intervalSeconds?: number;
   timeoutSeconds?: number;