reorganize subcommands into logical groups

60+ flat subcommands grouped into:
- Core (daily use): search, render, write, history, tail, status, query, used, wrong, gap
- Node: delete, rename, list, edges, dump
- Journal: write, tail, enrich
- Graph: link, audit, spectral, etc.
- Agent: daemon, knowledge-loop, consolidate, digest, etc.
- Admin: init, health, fsck, import, export, etc.

Also: remove dead migration code (migrate.rs, Migrate/JournalTsMigrate commands),
update memory-search and poc-hook for new subcommand paths, update daemon systemd
template for `agent daemon` path.

poc-memory/src/bin/memory-search.rs

@@ -126,7 +126,7 @@ fn main() {
         if debug { println!("[memory-search] loading full context"); }
 
         // Load full memory context, chunk it, print first chunk, save rest
-        if let Ok(output) = Command::new("poc-memory").args(["load-context"]).output() {
+        if let Ok(output) = Command::new("poc-memory").args(["admin", "load-context"]).output() {
             if output.status.success() {
                 let ctx = String::from_utf8_lossy(&output.stdout).to_string();
                 if !ctx.trim().is_empty() {