defs.rs: async conversion, remove block_in_place

Convert resolve(), resolve_placeholders(), run_agent() to async.
Use memory_render/memory_query directly with .await instead of
block_in_place wrappers.

Propagate async to callers:
- config.rs: resolve(), load_session(), reload_for_model()
- identity.rs: load_memory_files(), assemble_context_message()
- oneshot.rs: run_one_agent()
- prompts.rs: agent_prompt()

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/oneshot.rs

@@ -260,7 +260,7 @@ impl AutoAgent {
             .map_err(|e| format!("config: {}", e))?;
         let personality = crate::config::reload_for_model(
             &app, &app.prompts.other,
-        ).map_err(|e| format!("config: {}", e))?;
+        ).await.map_err(|e| format!("config: {}", e))?;
 
         let agent = Agent::new(
             client, personality,
@@ -381,7 +381,7 @@ pub struct AgentResult {
 
 /// Run an agent. If keys are provided, use them directly (bypassing the
 /// agent's query). Otherwise, run the query to select target nodes.
-pub fn run_one_agent(
+pub async fn run_one_agent(
     store: &mut Store,
     agent_name: &str,
     count: usize,
@@ -406,7 +406,7 @@ pub fn run_one_agent(
         for step in &def.steps {
             let (prompt, extra_keys) = defs::resolve_placeholders(
                 &step.prompt, store, keys, count,
-            );
+            ).await;
             all_keys.extend(extra_keys);
             resolved_steps.push(prompts::ResolvedStep {
                 prompt,
@@ -420,7 +420,7 @@ pub fn run_one_agent(
         batch
     } else {
         let effective_count = def.count.unwrap_or(count);
-        defs::run_agent(store, &def, effective_count, &Default::default())?
+        defs::run_agent(store, &def, effective_count, &Default::default()).await?
     };
 
     // Base memory tools + extras from agent def (matching unconscious.rs pattern)