capnp_store: remove dead code, consolidate CRUD API

Dead code removed:
- rebuild_uuid_index (never called, index built during load)
- node_weight inherent method (all callers use StoreView trait)
- node_community (no callers)
- state_json_path (no callers)
- log_retrieval, log_retrieval_append (no callers; only _static is used)
- memory_dir_pub wrapper (just make memory_dir pub directly)

API consolidation:
- insert_node eliminated — callers use upsert_node (same behavior
  for new nodes, plus handles re-upsert gracefully)

AnyView StoreView dispatch compressed to one line per method
(also removes UFCS workaround that was needed when inherent
node_weight shadowed the trait method).

-69 lines net.

src/main.rs

@@ -1357,7 +1357,7 @@ fn cmd_import(args: &[String]) -> Result<(), String> {
         let resolved = if path.exists() {
             path
         } else {
-            let mem_path = capnp_store::memory_dir_pub().join(arg);
+            let mem_path = capnp_store::memory_dir().join(arg);
             if !mem_path.exists() {
                 eprintln!("File not found: {}", arg);
                 continue;
@@ -1401,7 +1401,7 @@ fn cmd_export(args: &[String]) -> Result<(), String> {
         }).collect()
     };
 
-    let mem_dir = capnp_store::memory_dir_pub();
+    let mem_dir = capnp_store::memory_dir();
 
     for file_key in &targets {
         match store.export_to_markdown(file_key) {
@@ -1455,7 +1455,7 @@ fn cmd_journal_write(args: &[String]) -> Result<(), String> {
         node.source_ref = src;
     }
 
-    store.insert_node(node)?;
+    store.upsert_node(node)?;
     store.save()?;
 
     let word_count = text.split_whitespace().count();