evaluate: fix agent prompt path, dedup affected nodes, add --dry-run

- Use CARGO_MANIFEST_DIR for agent file path (same as defs.rs)
- Dedup affected nodes extracted from reports
- --dry-run shows example comparison prompt without LLM calls

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/src/main.rs

@@ -574,6 +574,9 @@ enum AgentCmd {
         /// Model to use for comparison (haiku or sonnet)
         #[arg(long, default_value = "haiku")]
         model: String,
+        /// Show example comparison prompt without calling LLM
+        #[arg(long)]
+        dry_run: bool,
     },
 }
 
@@ -795,7 +798,8 @@ fn main() {
                 => cli::agent::cmd_fact_mine(&path, batch, dry_run, output.as_deref(), min_messages),
             AgentCmd::FactMineStore { path } => cli::agent::cmd_fact_mine_store(&path),
             AgentCmd::ReplayQueue { count } => cli::agent::cmd_replay_queue(count),
-            AgentCmd::Evaluate { samples, model } => cli::agent::cmd_evaluate_agents(samples, &model),
+            AgentCmd::Evaluate { samples, model, dry_run }
+                => cli::agent::cmd_evaluate_agents(samples, &model, dry_run),
         },
 
         // Admin