refactor(hive-c0re): group src-root files into submodules

stores/ (sqlite-backed host stores + db helper), stats/, agent_config/,
workers/ — pure git-mv moves; crate-root re-exports keep every
crate::<module> path compiling. flake_check stays at root (synchronous
approval-flow validation, not a background worker)

docs/persistence.md

@@ -47,7 +47,7 @@ header/targets split, and the per-agent power-intent registry:
 - `agent_power` — one tiny row per agent: `agent PK / wanted (up |
   offline) / updated_at` — the durable power *intent* behind the job
   queue's desired-state reconciliation
-  (`docs/coordinator.md::Job queue`; owner: `hive-c0re/src/power.rs`).
+  (`docs/coordinator.md::Job queue`; owner: `hive-c0re/src/stores/power.rs`).
   Written synchronously by every operator/agent power action
   (dashboard start/stop, `hivectl stop`, the MCP kill/start tools,
   spawn approval); read by `Reconcile` nodes and the boot reconcile.