digest: modernize generate_digest() to use agent infrastructure

- Load template from digest.agent def (drop prompts_dir fallback)
- Resolve standard {{node:...}} placeholders — digest agent now gets
  core-personality, memory-instructions, subconscious notes
- Call through call_for_def_multi() with agent def's temperature,
  priority, and tools instead of call_simple()
- Move tool filtering from api.rs into callers (call_for_def_multi,
  run_one_agent_inner) — api takes pre-filtered &[Tool] slice

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

src/subconscious/knowledge.rs

@@ -296,15 +296,14 @@ fn run_one_agent_inner(
     log: &(dyn Fn(&str) + Sync),
 ) -> Result<AgentResult, String> {
     let all_tools = crate::agent::tools::memory_and_journal_tools();
-    let effective_tools: Vec<String> = if def.tools.is_empty() {
-        all_tools.iter().map(|t| t.name.to_string()).collect()
+    let effective_tools: Vec<crate::agent::tools::Tool> = if def.tools.is_empty() {
+        all_tools
     } else {
-        all_tools.iter()
+        all_tools.into_iter()
             .filter(|t| def.tools.iter().any(|w| w == &t.name))
-            .map(|t| t.name.to_string())
             .collect()
     };
-    let tools_desc = effective_tools.join(", ");
+    let tools_desc = effective_tools.iter().map(|t| t.name).collect::<Vec<_>>().join(", ");
     let n_steps = agent_batch.steps.len();
 
     for key in &agent_batch.node_keys {