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/llm.rs

@@ -34,7 +34,16 @@ pub(crate) fn call_for_def_multi(
     bail_fn: Option<&(dyn Fn(usize) -> Result<(), String> + Sync)>,
     log: &(dyn Fn(&str) + Sync),
 ) -> Result<String, String> {
-    super::api::call_api_with_tools_sync(&def.agent, prompts, phases, def.temperature, def.priority, &def.tools, bail_fn, log)
+    // Filter tools based on AgentDef specification
+    let all_tools = crate::agent::tools::memory_and_journal_tools();
+    let effective_tools: Vec<crate::agent::tools::Tool> = if def.tools.is_empty() {
+        all_tools
+    } else {
+        all_tools.into_iter()
+            .filter(|t| def.tools.iter().any(|w| w == &t.name))
+            .collect()
+    };
+    super::api::call_api_with_tools_sync(&def.agent, prompts, phases, def.temperature, def.priority, &effective_tools, bail_fn, log)
 }