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)

hive-c0re/src/agent_config/mod.rs

@@ -0,0 +1,10 @@
+//! Per-agent configuration registries: tool groups, capabilities,
+//! topology (all JSON files under `/var/lib/hyperhive/meta/`) and the
+//! shared wire-protocol size limits. Each submodule is re-exported at
+//! the crate root, so `crate::topology::…` etc. keep working
+//! unchanged.
+
+pub mod capabilities;
+pub mod limits;
+pub mod tool_groups;
+pub mod topology;