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/lib.rs

@@ -13,7 +13,6 @@ pub mod similarity;
 pub mod spectral;
 pub mod lookups;
 pub mod query;
-pub mod migrate;
 pub mod transcript;
 pub mod neuro;
 pub mod counters;