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.

unshell-leaves/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "unshell-leaves"
+version.workspace = true
+edition.workspace = true
+description = "Application-layer UnShell leaves and client surfaces"
+
+[features]
+default = []
+endpoint = ["dep:portable-pty"]
+tui = []
+
+[dependencies]
+rkyv = { workspace = true }
+portable-pty = { workspace = true, optional = true }
+unshell = { workspace = true }
+
+[lints.rust]
+elided_lifetimes_in_paths = "warn"
+future_incompatible = { level = "warn", priority = -1 }
+nonstandard_style = { level = "warn", priority = -1 }
+rust_2018_idioms = { level = "warn", priority = -1 }
+rust_2021_prelude_collisions = "warn"
+semicolon_in_expressions_from_macros = "warn"
+unsafe_op_in_unsafe_fn = "warn"
+unused_import_braces = "warn"
+unused_lifetimes = "warn"
+trivial_casts = "allow"
+missing_docs = "warn"