P2 slice 1: one executable (D-22)

The server and the viewer are libraries with run(prog, args), returning
Exit(code) instead of ending the process; ledger-mcp and ledger-gui are
one-line shims (the live books keep using them until the cutover).
wanderbooks dispatches dev-stdio and gui to them in-process; a mode must
come first and owns its flags. The gui feature (default) leaves the
viewer out of the server-only build, which just server-only builds,
clippies, tests, and checks for window libraries. The viewer's mutation
recipe is retired (owner, 2026-10-18); its two musts are tested
directly. Two review rounds; mutation on the diff (docs/testing.md).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-cli/Cargo.toml

@@ -10,6 +10,16 @@ description = "wanderbooks CLI: one command from nothing to a working books dire
 name = "wanderbooks"
 path = "src/main.rs"
 
+[features]
+default = ["gui"]
+# The viewer. Off in the server-only build for another machine (plan
+# D-22, P9), so a headless machine carries no window libraries.
+gui = ["dep:ledger-gui"]
+
+[dependencies]
+ledger-mcp = { path = "../ledger-mcp" }
+ledger-gui = { path = "../ledger-gui", optional = true }
+
 [dev-dependencies]
 chrono = "0.4"
 ledger-config = { path = "../ledger-config" }