polish(v0.6): put Sessions/Projects toggle on the filter row (kill whitespace)

The toggle sat on its own dedicated row, leaving a large empty band above the
project grid. On desktop (>=769px) float it top-right on the SAME row as the
filter box / launcher header: panels fill from the top (inset 0), launcher-head
reserves right padding for the pill. Mobile keeps the centred stacked toggle to
avoid overlapping the full-width filter on narrow screens. Also reclaim the
hidden key-bar's space on the home view (body.home-open #term { bottom: 0 }).

CSS-only (style.css is served directly). Verified in-browser: toggle and filter
share a row on Projects, no overlap with New/Manage on Sessions.

docs/PROGRESS_LOG.md

@@ -151,7 +151,7 @@
 - **状态**: `[x]` DONE。415 测试全绿 · 双 typecheck 干净 · `build:web` OK · 真浏览器验证通过。
 - **反馈**(用户): ① Sessions/Projects 段控在 UI 上"有点别扭"(原为两个独立描边方块浮在顶部);② 首页(Sessions/Projects 视图)底部那排终端快捷键栏没必要显示。
 - **修复**(纯前端,`public/style.css` + `public/tabs.ts`): ① `.home-seg` 重设计为 **iOS 风分段控件**——一个圆角"轨道"(`surface-2` 底 + 圆角 999px + 内边距)内含两个 pill 按钮,激活项填 Amber;`width:fit-content + margin:auto` 居中;去掉 first/last/only-child 圆角拼接;面板 `inset` 44→68px 适配新高度。② `TabApp.updateHomeView` 在显示首页时给 `document.body` 加 `home-open` 类,CSS `body.home-open #keybar{display:none}` 隐藏键栏;打开 tab(终端激活)即恢复。
-- **验证**: `npx tsc`(双)干净;`npx vitest run` 415/415;真浏览器:Projects 视图段控为圆角分段 pill(Projects 高亮)、键栏隐藏、83 卡片正常;开 tab 后键栏恢复。
+- **追加**(用户反馈"段控独占一行、空白太多"): 桌面端(`@media min-width:769px`)把段控 `position:absolute` 浮到**右上角**,与过滤框/启动器表头**同一行**;面板 `inset` 归 0(从顶部铺满),`.launcher-head` 留 240px 右内边距避开段控;移动端保持居中堆叠(防止与全宽过滤框重叠)。另:首页隐藏键栏时 `body.home-open #term{bottom:0}` 收回键栏占位。纯 CSS(`style.css` 直出,无需打包)。真浏览器实测:Projects 段控与过滤框同行(seg.top 56 / filter.top 62)、卡片在其下;Sessions 视图段控不与 New/Manage 重叠。
 - **commit**: (本次提交)
 
 ### 2026-06-30 · v0.6 UX 修复 — 会话内无法返回 Projects 首页