poc-memory agent run --debug: dump prompt and response

Add --debug flag that prints the full prompt and LLM response to
stdout, making it easy to iterate on agent prompts. Also adds
prompt field to AgentResult so callers can inspect what was sent.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poc-memory/src/agents/knowledge.rs

@@ -548,6 +548,7 @@ pub fn resolve_naming(
 
 /// Result of running a single agent through the common pipeline.
 pub struct AgentResult {
+    pub prompt: String,
     pub output: String,
     pub actions: Vec<Action>,
     pub no_ops: usize,
@@ -693,6 +694,7 @@ pub fn run_one_agent(
     }
 
     Ok(AgentResult {
+        prompt: agent_batch.prompt,
         output,
         actions,
         no_ops,