journal: split out as standalone agent, add {{bash:}} placeholder

Journal was step 5 of the surface-observe pipeline but never ran
because the bail check stopped the pipeline before reaching it.

Split into its own agent with:
- {{conversation:50000}} for recent conversation
- {{bash:poc-memory tail -p surface-observe 10}} for observe context
- {{latest_journal}} for previous entry continuity

Add generic {{bash:COMMAND}} placeholder to agent template resolver
so agents can include shell command output in their prompts.

Remove journal phase from surface-observe.agent (now 4 steps).

src/subconscious/defs.rs

@@ -570,6 +570,22 @@ fn resolve(
             Some(Resolved { text, keys })
         }
 
+        // bash:COMMAND — run a shell command and include its stdout
+        _ if name.starts_with("bash:") => {
+            let cmd = &name[5..];
+            let output = std::process::Command::new("bash")
+                .args(["-c", cmd])
+                .output();
+            let text = match output {
+                Ok(o) if o.status.success() =>
+                    String::from_utf8_lossy(&o.stdout).to_string(),
+                Ok(o) => format!("(command failed: {})",
+                    String::from_utf8_lossy(&o.stderr).trim()),
+                Err(e) => format!("(command error: {})", e),
+            };
+            Some(Resolved { text, keys: vec![] })
+        }
+
         _ => None,
     }
 }