journal: remove all stringly-typed key patterns, use NodeType

- journal_new: key is slugified title (agent names things properly)
- journal_tail: sort by created_at (immutable), not timestamp (mutable)
- journal_update: find latest by created_at
- {{latest_journal}}: query by NodeType::EpisodicSession, not "journal" key
- poc-memory journal write: requires a name argument
- Removed all journal#j-{timestamp}-{slug} patterns from:
  - prompts.rs (rename candidates)
  - graph.rs (date extraction, organize skip list)
  - cursor.rs (date extraction)
  - store/mod.rs (doc comment)
- graph.rs organize: filter by NodeType::Semantic instead of key prefix
- cursor.rs: use created_at for date extraction instead of key parsing

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

src/subconscious/prompts.rs

@@ -243,10 +243,10 @@ pub fn format_pairs_section(
 
 pub fn format_rename_candidates(store: &Store, count: usize) -> (Vec<String>, String) {
     let mut candidates: Vec<(&str, &crate::store::Node)> = store.nodes.iter()
-        .filter(|(key, _)| {
+        .filter(|(key, node)| {
             if key.starts_with("_facts-") { return true; }
             if key.len() < 60 { return false; }
-            if key.starts_with("journal#j-") { return true; }
+            if node.node_type == crate::store::NodeType::EpisodicSession { return true; }
             if key.starts_with("_mined-transcripts#f-") { return true; }
             false
         })
@@ -271,9 +271,9 @@ pub fn format_rename_candidates(store: &Store, count: usize) -> (Vec<String>, St
     let mut out = String::new();
     out.push_str(&format!("## Nodes to rename ({} of {} candidates)\n\n",
         candidates.len(),
-        store.nodes.keys().filter(|k| k.starts_with("_facts-") ||
+        store.nodes.iter().filter(|(k, n)| k.starts_with("_facts-") ||
             (k.len() >= 60 &&
-             (k.starts_with("journal#j-") || k.starts_with("_mined-transcripts#f-")))).count()));
+             (n.node_type == crate::store::NodeType::EpisodicSession || k.starts_with("_mined-transcripts#f-")))).count()));
 
     for (key, node) in &candidates {
         out.push_str(&format!("### {}\n", key));