fix(tui): make ShellKind's dead_code expectations platform-accurate

`Test (windows-latest)` has not compiled on this branch: five errors, all in
shell_dispatcher.rs, and all the same mistake seen from two sides.

Which `ShellKind` variants are live is exactly a platform split. `detect`
builds `Pwsh`, `WindowsPowerShell`, `Cmd` and `Bash` inside `cfg(windows)`
(:446-468) and `Sh` and `Custom` inside `cfg(not(windows))` (:471-504). The
annotations from the #5587 sweep were written from the unix side only:
the four Windows variants carried an unconditional
`cfg_attr(not(test), expect(dead_code))`, and `Sh`/`Custom` carried none.

On unix that is right and CI stayed green. On Windows both halves invert:
the four expectations go unfulfilled because those variants *are* constructed,
and `Sh`/`Custom` become genuinely unconstructed. `expect` is an error when
unfulfilled, so the lib failed to compile before a single test ran.

Each annotation now names the platform it is dead on. No variant is silenced
on a platform where it is live, so the ratchet #5587 installed still bites on
both.

Verification, stated honestly: `cargo check -p codewhale-tui --lib --locked`
is clean on unix, and the full CI clippy gate
(`--workspace --all-targets --all-features -D warnings`) exits 0. The Windows
half could NOT be checked locally — `cargo check --target
x86_64-pc-windows-msvc` cannot build `ring`, whose build script needs an
MSVC-targeting C compiler this host does not have. The Windows claim rests on
the cfg structure above, and CI is its first real test.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

crates/tui/src/shell_dispatcher.rs

@@ -40,21 +40,28 @@ pub(crate) mod test_env_lock;
 /// The concrete shell that the dispatcher will use.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ShellKind {
+    // Which variants are live is exactly a platform split: `detect` builds the
+    // four Windows shells under `cfg(windows)` and `Sh`/`Custom` under
+    // `cfg(not(windows))`. So each `expect(dead_code)` has to name the platform
+    // it is dead on, or it fires as unfulfilled on the other one — which is how
+    // the Windows build broke while unix stayed green.
     /// PowerShell 7+ (`pwsh.exe`).
-    #[cfg_attr(not(test), expect(dead_code))]
+    #[cfg_attr(all(not(test), not(windows)), expect(dead_code))]
     Pwsh,
     /// Windows PowerShell 5.1 (`powershell.exe`).
-    #[cfg_attr(not(test), expect(dead_code))]
+    #[cfg_attr(all(not(test), not(windows)), expect(dead_code))]
     WindowsPowerShell,
     /// Command Prompt (`cmd.exe`).
-    #[cfg_attr(not(test), expect(dead_code))]
+    #[cfg_attr(all(not(test), not(windows)), expect(dead_code))]
     Cmd,
     /// Unix `/bin/sh` fallback.
+    #[cfg_attr(all(not(test), windows), expect(dead_code))]
     Sh,
     /// Bash — detected via `$SHELL` on WSL/Git Bash, or constructed explicitly.
-    #[cfg_attr(not(test), expect(dead_code))]
+    #[cfg_attr(all(not(test), not(windows)), expect(dead_code))]
     Bash,
     /// The exact shell executable selected by Unix `$SHELL`.
+    #[cfg_attr(all(not(test), windows), expect(dead_code))]
     Custom { binary: String, flag: String },
 }