refactor: merge workspace (core/ + ui/) into a single flat binary crate

integrate CLI into main.rs, no lib.rs by design (YAGNI)

justfile

@@ -60,13 +60,9 @@ check-json: (check '--message-format=json')
 test *args:
     cargo test --workspace {{args}}
 
-# Runs the COSMIC UI application
+# Runs the application (no args = COSMIC UI, with args = CLI mode)
 run *args:
-    env RUST_BACKTRACE=full cargo run --release -p noctua_ui {{args}}
-
-# Runs the CLI test harness (core only, no UI deps)
-run-cli *args:
-    env RUST_BACKTRACE=full cargo run --example cli -p noctua_core {{args}}
+    env RUST_BACKTRACE=full cargo run --release {{args}}
 
 # Installs files
 install: