feat: fixed-width tab hover with sliding title, pop-out button now opt-in

Hovering a session tab no longer grows it. The three per-tab icons now
live in a .tab-actions wrapper that overlays the tab's right edge on
hover-capable devices: the icons slide in while the title (and any
badges) slide left by a per-tab --tab-slide distance computed in
_applyTabHoverSlide(), clipped at the left edge of .tab-info so the
readable tail (the :comment suffix) stays visible. Keyboard focus
reveals the overlay via :has(:focus-visible), so a mouse click on the
gear does not pin it open. Touch devices keep the previous in-flow
behavior (the wrapper adds no width in flow, and the legacy tap-reveal
rules are preserved under @media (hover: none)).

The open-in-a-new-window (pop-out) button is now hidden by default and
opt-in via App Settings -> Tab Bar -> "Pop-out Button on Tabs"
(showTabDetachButton, per-device, absent from SettingsUpdateSchema like
the other display keys). A tab whose session is already detached keeps
its icon as the re-focus affordance regardless of the setting.

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

src/web/public/i18n.js

@@ -227,6 +227,7 @@
     'Redraw Terminal Button': '重绘终端按钮',
     'Tab Bar': '标签栏',
     'Tall Tabs (Name + Folder)': '双行标签（名称 + 文件夹）',
+    'Pop-out Button on Tabs': '标签页弹出窗口按钮',
     Panels: '面板',
     Monitor: '监视器',
     'Project Insights': '项目洞察',