feat: add lux to PATH on shell entry

- Build release binary when entering nix shell
- Add target/release to PATH automatically
- Update shell help to show lux commands

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.nix

@@ -30,6 +30,10 @@
           RUST_SRC_PATH = "${rustToolchain}/lib/rustlib/src/rust/library";
 
           shellHook = ''
+            # Build and add lux to PATH
+            cargo build --release --quiet 2>/dev/null
+            export PATH="$PWD/target/release:$PATH"
+
             printf "\n"
             printf "  \033[1;35m╦  ╦ ╦╦ ╦\033[0m\n"
             printf "  \033[1;35m║  ║ ║╔╣\033[0m\n"
@@ -38,10 +42,13 @@
             printf "  Functional language with first-class effects\n"
             printf "\n"
             printf "  \033[1mCommands:\033[0m\n"
+            printf "    lux                     Start the REPL\n"
+            printf "    lux \033[3m<file.lux>\033[0m          Run a file\n"
+            printf "    lux compile \033[3m<file.lux>\033[0m  JIT compile and run\n"
+            printf "\n"
+            printf "  \033[1mDevelopment:\033[0m\n"
             printf "    cargo build     Build the compiler\n"
-            printf "    cargo run       Start the REPL\n"
             printf "    cargo test      Run tests\n"
-            printf "    cargo run -- \033[3m<file.lux>\033[0m  Run a file\n"
             printf "\n"
           '';
         };