Merge lh-ui refinement wave (feat/ui-polish @ 8163437) into main

11 commits on fbeca36: minimal-color rounds 1-2 (phase color retired,
the braille spinner is the one working indicator; the chip is label-only),
typography rounds 1-5 (three-font rule enforced — CMU titles, Source Sans
session titles, JetBrains mono; snapped type ladder in globals.css with
the xxs rung merged into xs; lh-input caret at the font-metric floor;
session titles at prose size, message counts and active-row weight dropped,
ISO dates), header rounds 6/6b/6c/6d (60px top bar aligned to the sidebar
LH band; the open-sidebar toggle matches the close glyph at size-4 both
ways; SidebarToggle always-mounted with a lockstep animated slot — no more
one-frame title jump; title at text-3xl).

Semantic change folded in: `busy` in the chats list now means exactly "a
teach turn is in flight" — background jobs no longer spin the session row
(the sidebar's Background agents section is their channel).

Merge fallout fixed in the merge: components/graph-coverage.tsx (main's
coverage panel) held the last three text-xxs uses; with the rung deleted
they silently lost their size — mechanically swapped to text-xs, matching
lh-ui's own swap in graph-context-marker.tsx.

No file overlap with main's waves since fbeca36 (extraction coverage,
lh-graph merge, world-scale bake) — clean auto-merge. Gates: typecheck,
eslint, 496/496 tests, build. Live-verified on the dev server: 60px
header with 32px CMU title, label-only chip, snapped ladder active
(--lh-prose-size 16px, no --text-xxs rule anywhere), sidebar rows with
ISO dates, animated sidebar toggle with no header jump.

src/core/contracts/chat.ts

@@ -286,10 +286,12 @@ export interface ChatSummary {
 }
 
 /** The sidebar's session row: a summary + live liveness. The chats list
- *  route attaches `busy` from the turn-liveness registry and the job store
- *  (a running turn OR a background job = the session is working). The store
- *  itself can't see liveness (import law: store never imports server),
- *  hence the split at exactly the record/liveness seam. */
+ *  route attaches `busy` from the turn-liveness registry ONLY — a running
+ *  teach turn (owner, minimal-color round: background jobs no longer
+ *  count; the sidebar's Background agents section is their channel, and
+ *  the row spinner means exactly "a turn is in flight"). The store itself
+ *  can't see liveness (import law: store never imports server), hence the
+ *  split at exactly the record/liveness seam. */
 export interface ChatListItem extends ChatSummary {
 	busy: boolean;
 }