Split protocol and leaf surfaces into crates

Move the protocol runtime into unshell-protocol and remote shell leaf code into unshell-leaves so endpoint and TUI roles can compile independently without circular dependencies.

Cargo.toml

@@ -5,6 +5,8 @@ members = [
     "ush-obfuscate",
     "base62",
     "unshell-macros",
+    "unshell-protocol",
+    "unshell-leaves",
     "treetest",
 ]
 resolver = "2"
@@ -27,6 +29,8 @@ quote             = "1.0.45"
 proc-macro2       = "1.0.106"
 portable-pty      = "0.9.0"
 unshell          = { path = "." }
+unshell-protocol = { path = "./unshell-protocol" }
+unshell-leaves   = { path = "./unshell-leaves" }
 # ush-obfuscate = { path = "./ush-obfuscate" }
 # base62        = { path = "./base62" }
 
@@ -50,7 +54,10 @@ chrono            = { workspace = true, optional = true }
 # ush-obfuscate     = { workspace = true }
 static_init       = { workspace = true }
 unshell-macros    = { path = "./unshell-macros" }
-portable-pty      = { workspace = true }
+unshell-protocol  = { workspace = true }
+
+[dev-dependencies]
+unshell-leaves = { workspace = true, features = ["endpoint"] }
 
 [[example]]
 name = "leaf_derive"