refactor(#1865): rename agent_server module to socket_server

Pure rename ahead of the agent+manager server consolidation: the
per-agent socket dispatcher already hosts the shared dispatch and all
lifecycle handlers, and will absorb the manager-only handlers next, so
`agent_server` becomes a misnomer. No logic change — git mv plus a
mechanical `agent_server` -> `socket_server` rename across refs.

hive-c0re/src/reminder_scheduler.rs

@@ -130,7 +130,7 @@ fn inline_fallback(req_path: &str, reason: &str, message: &str) -> String {
 /// Persist `message` to `host_path` with the symlink-escape defenses
 /// described in the module docs. Returns `Ok(())` on success, or a
 /// human-readable reason string on any failure (caller logs +
-/// inline-falls-back). `pub` because `agent_server::handle_remind`
+/// inline-falls-back). `pub` because `socket_server::handle_remind`
 /// reuses it for the at-remind-time auto-file path.
 pub fn write_payload(agent: &str, host_path: &Path, message: &str) -> Result<(), String> {
     let Some(parent) = host_path.parent() else {
@@ -186,7 +186,7 @@ pub fn container_state_prefix(agent: &str) -> String {
 /// validating that it lives under the agent's own state subtree, has
 /// a non-empty relative tail, and doesn't try to traverse out via
 /// `..`. Returns the host `PathBuf` on success, or a human-readable
-/// reason string on rejection. `pub` so `agent_server::handle_remind`
+/// reason string on rejection. `pub` so `socket_server::handle_remind`
 /// can reuse it for the at-remind-time auto-file path.
 pub fn resolve_host_path(agent: &str, req_path: &str) -> Result<PathBuf, String> {
     let prefix = container_state_prefix(agent);