feat(tabs,header): group tabs by state and add header stats styles (#426)

Two directions from Discussion #426, each a per-device setting and the
new default.

Tab Grouping (tabGrouping: 'state' | 'none', default 'state', option C):
tabs are grouped needs you (red, plus failed sessions), waiting (yellow),
working and idle (also ended, exited panes and web tabs), most urgent on
top. The desktop header strip draws a row per group with its label and
count in a left gutter; the flat vertical rail and the sidebar draw a
section per group; tablets keep their scrolling row with inline dividers;
phones keep the chip row in group order without headings. Classification
is the home screens' own (_mobileOverviewState/_mobileOverviewExit), the
fold into four groups is pure in CodemanTabTriage (constants.js). It is
flex `order` plus aria-hidden heading/break elements reconciled in place
after both render paths, never a DOM reorder, so Alt+N, the keyboard walk
and drag keep reading tab order; a drop is refused across groups. Named
groups in the vertical rail take precedence.

Header Stats Style (headerStatsStyle: 'classic' | 'compact' | 'tiles',
default 'tiles', option G): tiles give WS, CPU, MEM and each plan window
a label-over-value tile with a bar underneath; compact is one WS/CPU/MEM
pill with sparklines plus a plan-ring pill; classic is the header as
before. Desktop only (classic below 768px and in solo windows). The
clustered styles move #connectionIndicator into #headerSystemStats and
WS stays out of a hidden System Stats pill. The extra parts are always
rendered and hidden by default in CSS, so classic is unchanged.

Tests: test/tab-triage.test.ts, test/header-stats-style.test.ts; three
source pins in test/tab-rail-order.test.ts follow renamed lines.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/public/mobile.css

@@ -755,6 +755,14 @@ html.mobile-init .file-browser-panel {
     font-weight: 500;
   }
 
+  /* Grouped by state (tabGrouping), the phone strip keeps its one scrolling
+     row: the tabs still come in state order, most urgent first, but the
+     headings would cost chips and the dots already say which state is which.
+     The phone overview is where the labelled sections live. */
+  :where(.header) .tab-triage-head {
+    display: none;
+  }
+
   /* Only the active tab shows its action icons on a phone (see below), so on
      every other tab the container is empty but still a flex item, and its gap
      made the chip visibly wider on the right than on the left. */