feat(setup): paint card and log bodies in brand cyan

Adds a `brandBody` helper in setup/lib/theme.ts that wraps prose in
brand cyan (#2BB7CE), with the same TTY/NO_COLOR/truecolor gating used
by `brand`/`brandBold`/`brandChip`. The helper splits multi-line input
and colors each line independently so the SGR sequence doesn't bleed
across clack's gutter prefix.

Routing:
  - `note()` (the un-dim card wrapper from #2095) now passes
    `brandBody` as its `format` callback, so card bodies render
    cyan line-by-line.
  - Every prose `p.log.{message,info,success,step,warn}` call in the
    setup flow wraps its body argument in `brandBody`. Calls whose
    body is explicitly `k.dim(...)` (failure transcript tails, log
    paths, claude-assist response previews) are left alone — those
    are the "preview/debug" cases the dim-policy comment in
    theme.ts already carves out.
  - Spinner-finish lines in windowed-runner / claude-assist color
    only the message portion; the `(5s)` elapsed suffix stays dim.

Brand cyan accents (chips, wordmark, inline emphasis) are unchanged.
This PR only adds the body color.

A follow-up will add OSC 11 dark/light detection so light-mode
terminals get a brand blue (#2b6fdc) variant — opt-in upgrade with
no regression for the dark-mode default.

setup/lib/claude-handoff.ts

@@ -27,7 +27,7 @@ import { execSync, spawn } from 'child_process';
 import * as p from '@clack/prompts';
 import k from 'kleur';
 
-import { note } from './theme.js';
+import { brandBody, note } from './theme.js';
 
 export interface HandoffContext {
   /** Channel this handoff is happening in (e.g., 'teams'). */
@@ -64,7 +64,7 @@ export interface HandoffContext {
 export async function offerClaudeHandoff(ctx: HandoffContext): Promise<boolean> {
   if (!isClaudeUsable()) {
     p.log.warn(
-      "Claude isn't installed yet — can't hand you off here. Finish setup first, then retry.",
+      brandBody("Claude isn't installed yet — can't hand you off here. Finish setup first, then retry."),
     );
     return false;
   }
@@ -93,7 +93,7 @@ export async function offerClaudeHandoff(ctx: HandoffContext): Promise<boolean>
       { stdio: 'inherit' },
     );
     child.on('close', () => {
-      p.log.success("Back from Claude. Let's continue.");
+      p.log.success(brandBody("Back from Claude. Let's continue."));
       resolve(true);
     });
     child.on('error', () => {