feat: tab action icons on the active tab only, middle-click closes tabs

Rework of the previous hover-overlay approach after feedback: sliding the
title under incoming icons made names hard to read, and icons appearing
under the cursor caused accidental gear/close clicks while switching tabs.

Now the gear/pop-out/close icons expand in flow on the ACTIVE tab only.
Selection is a deliberate click, so the strip's geometry never changes
while the pointer is aiming at a tab; hovering a background tab changes
nothing (the full title stays readable) and a stray click can only switch
sessions. Middle-click closes any tab (session tabs via the existing
close-confirm modal, web tabs via closeWebviewTab), matching browser
muscle memory so background tabs still close in one action.

The pop-out button stays opt-in via App Settings -> Tab Bar (per-device
showTabDetachButton, default off), and a detached tab keeps its icon as
the re-focus affordance. Phone layouts already used the active-only
pattern; tablets keep their always-visible touch fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/settings-ui.js

@@ -2003,7 +2003,7 @@ Object.assign(CodemanApp.prototype, {
     const settings = this.loadAppSettingsFromStorage();
     const defaults = this.getDefaultSettings();
 
-    // Tab pop-out (open-in-new-window) button — opt-in (App Settings → Tab Bar,
+    // Tab pop-out (open-in-new-window) button: opt-in (App Settings → Tab Bar,
     // default OFF, per-device). Mirrored as a class on <html>: styles.css hides
     // .tab-detach without it (a tab that is already detached keeps its icon as
     // the re-focus affordance for the popped-out window).