docs(readme): 未知子命令的提示改成 unlucky-launcher --help（M82 r4 复审 P2）

两版 README 的「未知子命令是错误，不是开窗」一段写的是提示 `ull --help`，与真实输出相反：
GUI 二进制跑出来是 `unlucky-launcher --help`（只有 `ull` 自己跑才是 `ull --help`），
而且同文 87/77 行已经写着「自称的名字跟着你敲的那个二进制走」——正文自相矛盾。

只改这两处；全文其余 `ull` 都是指 `ull` 那个产物本身（对照表、§ 说明、`ull --help` 的对比句），
按语境保留。

README.md

@@ -110,8 +110,8 @@ The rule is deliberately narrow, so nothing that used to work changed meaning:
   still opens the GUI.
 
 **Unknown subcommands are an error, not a GUI launch**: `unlucky-launcher lst` prints
-"未知命令 `lst`", hints `ull --help`, and exits 1. Silently opening a window would tell a script
-that its typo took effect. The subcommand table itself lives in exactly one place —
+"未知命令 `lst`", hints `unlucky-launcher --help`, and exits 1. Silently opening a window would tell
+a script that its typo took effect. The subcommand table itself lives in exactly one place —
 `crates/cli/src/cli/parse.rs` — so both GUI binaries and `ull` accept the same set by construction.
 
 ## Module map