remove Category from the type system

Category was a manually-assigned label with no remaining functional
purpose (decay was the only behavior it drove, and that's gone).
Remove the enum, its methods, category_counts, the --category search
filter, and all category display. The field remains in the capnp
schema for backwards compatibility but is no longer read or written.

Status and health reports now show NodeType breakdown (semantic,
episodic, daily, weekly, monthly) instead of categories.

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

src/main.rs

@@ -135,7 +135,7 @@ fn usage() {
     eprintln!("poc-memory v0.4.0 — graph-structured memory store
 
 Commands:
-  search QUERY [--expand] [--category CAT]  Search memory (AND logic)
+  search QUERY [--expand]  Search memory (AND logic)
   init                      Scan markdown files, index all memory units
   migrate                   Migrate from old weights.json system
   health                    Report graph metrics (CC, communities, small-world)
@@ -224,55 +224,24 @@ Search memory using spreading activation (AND logic across terms).
 
 Options:
   --expand            Show 15 results instead of 5, plus spectral neighbors
-  --category CAT      Filter results to category: core, tech, gen, obs, task
   --help, -h          Show this help
 
 Examples:
   poc-memory search irc connection
-  poc-memory search bcachefs transaction --expand
-  poc-memory search rust --category tech");
+  poc-memory search bcachefs transaction --expand");
         return Ok(());
     }
 
     let expand = args.iter().any(|a| a == "--expand");
 
-    let category_filter: Option<String> = {
-        let mut cat = None;
-        let mut iter = args.iter();
-        while let Some(a) = iter.next() {
-            if a == "--category" {
-                cat = iter.next().cloned();
-                break;
-            }
-        }
-        cat
-    };
-
     let query: String = args.iter()
-        .filter(|a| *a != "--expand" && *a != "--category")
-        .scan(false, |skip_next, a| {
-            if *skip_next { *skip_next = false; return Some(None); }
-            if a == "--category" { *skip_next = true; return Some(None); }
-            Some(Some(a.as_str()))
-        })
-        .flatten()
+        .filter(|a| *a != "--expand")
+        .map(|a| a.as_str())
         .collect::<Vec<_>>()
         .join(" ");
 
     let view = store::AnyView::load()?;
-    let mut results = search::search(&query, &view);
-
-    // Filter by category if requested
-    if let Some(ref cat_str) = category_filter {
-        let cat = store::Category::from_str(cat_str)
-            .ok_or_else(|| format!("Unknown category '{}' (use: core, tech, gen, obs, task)", cat_str))?;
-        let store = store::Store::load()?;
-        results.retain(|r| {
-            store.nodes.get(&r.key)
-                .map(|n| n.category.label() == cat.label())
-                .unwrap_or(false)
-        });
-    }
+    let results = search::search(&query, &view);
 
     if results.is_empty() {
         eprintln!("No results for '{}'", query);
@@ -459,16 +428,19 @@ fn cmd_status() -> Result<(), String> {
     let store = store::Store::load()?;
     let node_count = store.nodes.len();
     let rel_count = store.relations.len();
-    let categories = store.category_counts();
+
+    let mut episodic = 0usize;
+    let mut semantic = 0usize;
+    for n in store.nodes.values() {
+        if matches!(n.node_type, store::NodeType::Semantic) {
+            semantic += 1;
+        } else {
+            episodic += 1;
+        }
+    }
 
     println!("Nodes: {}  Relations: {}", node_count, rel_count);
-    println!("Categories: core={} tech={} gen={} obs={} task={}",
-        categories.get("core").unwrap_or(&0),
-        categories.get("tech").unwrap_or(&0),
-        categories.get("gen").unwrap_or(&0),
-        categories.get("obs").unwrap_or(&0),
-        categories.get("task").unwrap_or(&0),
-    );
+    println!("Types: semantic={} episodic={}", semantic, episodic);
 
     let g = store.build_graph();
     println!("Graph edges: {}  Communities: {}",
@@ -1058,8 +1030,8 @@ fn cmd_trace(args: &[String]) -> Result<(), String> {
 
     // Display the node itself
     println!("=== {} ===", resolved);
-    println!("Type: {:?}  Category: {}  Weight: {:.2}",
-        node.node_type, node.category.label(), node.weight);
+    println!("Type: {:?}  Weight: {:.2}",
+        node.node_type, node.weight);
     if !node.source_ref.is_empty() {
         println!("Source: {}", node.source_ref);
     }