modules: split services and the ircd link into external crates

nickserv, chanserv and the InspIRCd protocol move out of the binary into their
own workspace crates (fedserv-nickserv, fedserv-chanserv, fedserv-inspircd),
each depending only on fedserv-api. human_time and the branded account emails
move into the SDK crate so a module needs nothing from core; the engine keeps
its own inherent methods and builds emails via fedserv-api too. The bin now
constructs each module from its crate instead of an in-tree #[path] include.
Proves the SDK is self-sufficient: a third-party module is the same shape.

src/proto.rs

@@ -0,0 +1,4 @@
+// The normalized protocol vocabulary lives in the fedserv-api SDK crate;
+// re-exported so the engine keeps referring to it as `crate::proto::*`. The
+// concrete ircd link (InspIRCd) is an external module crate, not part of core.
+pub use fedserv_api::{NetAction, NetEvent, Protocol, RegReply};