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/theme.ts

@@ -51,6 +51,22 @@ export function accentGreen(s: string): string {
   return k.green(s);
 }
 
+/**
+ * Format an elapsed-time duration (in milliseconds) for the spinner
+ * suffixes setup writes everywhere. Sub-minute durations stay in plain
+ * seconds (`47s`); once the timer crosses 60 seconds we switch to the
+ * `Xm Ys` form (`2m 34s`) so a long step doesn't read as `247s` or
+ * similar. The format is consistent above 60s — `4m 0s` over `4m` —
+ * so live spinner output doesn't change shape at every whole minute.
+ */
+export function fmtDuration(ms: number): string {
+  const totalSec = Math.round(ms / 1000);
+  if (totalSec < 60) return `${totalSec}s`;
+  const m = Math.floor(totalSec / 60);
+  const s = totalSec % 60;
+  return `${m}m ${s}s`;
+}
+
 /**
  * Brand body color for setup-flow prose. Used for card bodies (via the
  * `note()` formatter) and `p.log.*` body arguments — anywhere the