feat(setup): switch elapsed-time suffixes to "Xm Ys" past 60s

Adds a `fmtDuration(ms)` helper in `setup/lib/theme.ts` that returns
`47s` under a minute and `1m 34s` from 60s onward, then routes every
elapsed-time spinner suffix in the setup flow through it. Replaces
the inline `Math.round((Date.now() - start) / 1000)` + `(${elapsed}s)`
pattern at every site.

Format is consistent past 60s — `1m 0s` over `1m` — so the live
spinner doesn't change shape at every whole-minute crossing.

Sites updated: setup/auto.ts, setup/lib/{runner,tz-from-claude,
claude-assist}.ts, and setup/channels/{signal,whatsapp,telegram,
discord,slack}.ts. Pre-allocated suffix budgets in `fitToWidth`
calls bumped from `' (999s)'` to `' (99m 59s)'` so long-running
steps don't blow past the reserved width.

setup/lib/claude-assist.ts

@@ -28,7 +28,7 @@ import * as p from '@clack/prompts';
 import k from 'kleur';
 
 import { ensureAnswer } from './runner.js';
-import { brandBody, fitToWidth, note } from './theme.js';
+import { brandBody, fitToWidth, fmtDuration, note } from './theme.js';
 
 export interface AssistContext {
   stepName: string;
@@ -295,9 +295,8 @@ async function queryClaudeUnderSpinner(
     // Move cursor back to the start of the block (WINDOW_SIZE + 1 = header + window).
     out.write(`\x1b[${WINDOW_SIZE + 1}A`);
 
-    const elapsed = Math.round((Date.now() - start) / 1000);
     const icon = SPINNER_FRAMES[frameIdx % SPINNER_FRAMES.length];
-    const suffix = ` (${elapsed}s)`;
+    const suffix = ` (${fmtDuration(Date.now() - start)})`;
     const header = fitToWidth('Asking Claude to diagnose…', suffix);
     out.write(`\x1b[2K${k.cyan(icon)}  ${header}${k.dim(suffix)}\n`);
 
@@ -355,8 +354,7 @@ async function queryClaudeUnderSpinner(
       clearBlock();
       out.write(SHOW_CURSOR);
       process.off('exit', restoreCursorOnExit);
-      const elapsed = Math.round((Date.now() - start) / 1000);
-      const suffix = ` (${elapsed}s)`;
+      const suffix = ` (${fmtDuration(Date.now() - start)})`;
       if (kind === 'ok') {
         p.log.success(`${brandBody(fitToWidth('Claude replied.', suffix))}${k.dim(suffix)}`);
         resolve(payload);