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/tz-from-claude.ts

@@ -17,7 +17,7 @@ import * as p from '@clack/prompts';
 import k from 'kleur';
 
 import { isValidTimezone } from '../../src/timezone.js';
-import { fitToWidth } from './theme.js';
+import { fitToWidth, fmtDuration } from './theme.js';
 
 export function claudeCliAvailable(): boolean {
   try {
@@ -44,18 +44,16 @@ export async function resolveTimezoneViaClaude(
   const s = p.spinner();
   const start = Date.now();
   const label = 'Looking up that timezone…';
-  s.start(fitToWidth(label, ' (999s)'));
+  s.start(fitToWidth(label, ' (99m 59s)'));
   const tick = setInterval(() => {
-    const elapsed = Math.round((Date.now() - start) / 1000);
-    const suffix = ` (${elapsed}s)`;
+    const suffix = ` (${fmtDuration(Date.now() - start)})`;
     s.message(`${fitToWidth(label, suffix)}${k.dim(suffix)}`);
   }, 1000);
 
   const reply = await queryClaude(prompt);
 
   clearInterval(tick);
-  const elapsed = Math.round((Date.now() - start) / 1000);
-  const suffix = ` (${elapsed}s)`;
+  const suffix = ` (${fmtDuration(Date.now() - start)})`;
 
   const resolved = reply ? extractTimezone(reply) : null;
   if (resolved) {