Minimal-color round 1 (owner): phase color retired — the braille spinner is the one working indicator

Nothing exists purely for decoration: phase color-coding is retired
app-wide (phases only advance — every session ends Teaching — so
phase-as-signal was decoration with a one-time function), and what
state genuinely deserved — 'a turn is in flight' — is now carried by
MOTION alone, in the terminal's own glyph language.

- BrailleSpinner (components/braille-spinner.tsx): the canonical
  cli-spinner sequence (⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏) as exact dot bitmaps in a 2×4
  braille cell, 80ms/frame (800ms cycle). Pure CSS: one shared keyframes,
  frames staggered via animation-delay; no JS timer, no re-render per
  frame — cheaper than the old breathing dot. Static contexts (SSR,
  prefers-reduced-motion) show frame 0 — a legible glyph, not a blank.
- Sidebar rows: spinner ONLY while a teach turn is in flight; idle and
  question-pending render NOTHING (a resting state has no scan value —
  the meta line's 'Waiting for your answer' text carries it). The
  three-state phase dot (pulse/solid/hollow) and PHASE_FILL/RING maps
  are gone.
- Top bar PhaseChip: label-only pill; the old dot slot becomes the
  spinner's home while a turn is in flight (busy prop wired from
  ChatView's busy = localStream || turnInFlight). Transcript
  PhaseDividers drop phase colors for monochrome rules + labels.
- API narrowing (app/api/chats/route.ts + ChatListItem contract):
  busy = isTurnRunning ONLY — background jobs no longer count (the
  sidebar's Background agents section is their channel; a per-row
  spinner would double-signal them).
- globals.css: --phase-* tokens + lh-dot-breathe removed (dead after
  the sweep — no remaining users).

Live-verified: idle/pending rows render no indicator, /chat/new chip is
label-only, 10 CSSAnimations at 800ms with correct 80ms stagger, static
frame 0 under reduced motion. Gates: typecheck, lint, 470/470, build.

Lane crossings to flag at merge: app/api/chats/route.ts + the
ChatListItem contract comment (src/core) — the busy-semantics narrowing;
components/chat.tsx one-line busy prop.

components/chat.tsx

@@ -605,7 +605,7 @@ export function Chat({
 							Plan
 						</button>
 					)}
-					<PhaseChip phase={phases.at(-1) ?? "probe"} />
+					<PhaseChip phase={phases.at(-1) ?? "probe"} busy={busy} />
 				</header>
 
 				<div className="relative flex min-h-0 flex-1">