feat: enhance agent personality, tool guidance, and memory hygiene

- Expand communication style presets (professional, expressive, custom)
- Enrich SOUL.md with human-like tone and emoji-awareness guidance
- Add crash recovery and sub-task scoping guidance to AGENTS.md scaffold
- Add 'Use when / Don't use when' guidance to TOOLS.md and runtime prompts
- Implement memory hygiene system with configurable archiving and retention
- Add MemoryConfig options: hygiene_enabled, archive_after_days, purge_after_days, conversation_retention_days
- Archive old daily memory and session files to archive subdirectories
- Purge old archives and prune stale SQLite conversation rows
- Add comprehensive tests for new features

src/memory/mod.rs

@@ -1,5 +1,6 @@
 pub mod chunker;
 pub mod embeddings;
+pub mod hygiene;
 pub mod markdown;
 pub mod sqlite;
 pub mod traits;
@@ -21,6 +22,11 @@ pub fn create_memory(
     workspace_dir: &Path,
     api_key: Option<&str>,
 ) -> anyhow::Result<Box<dyn Memory>> {
+    // Best-effort memory hygiene/retention pass (throttled by state file).
+    if let Err(e) = hygiene::run_if_due(config, workspace_dir) {
+        tracing::warn!("memory hygiene skipped: {e}");
+    }
+
     match config.backend.as_str() {
         "sqlite" => {
             let embedder: Arc<dyn embeddings::EmbeddingProvider> =