feat(forms): country→timezone autoset, "Other" channel hint, polish

Client form: when nationality is picked and timezone empty, primary
IANA zone for the country is pre-filled (skips when user has chosen
a zone explicitly). When a contact's preferred channel is `'other'`,
the inline `Label` field flips to "Specify" / "e.g. Telegram, Signal"
so the rep records what the channel actually is.

Yacht form: replace the free-text 2-letter flag input with the shared
`CountryCombobox` so flags stay valid ISO codes.

User settings: timezone pre-populates from
`Intl.DateTimeFormat().resolvedOptions().timeZone` on first load
(was empty before); country change auto-fills timezone with the same
helper as the client form. Phone field upgraded to the shared
`<PhoneInput>` (country-flag dropdown + AsYouType formatter) seeded
from the page's country state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/clients/client-form.tsx

@@ -27,6 +27,7 @@ import { DedupSuggestionPanel } from '@/components/clients/dedup-suggestion-pane
 import { apiFetch } from '@/lib/api/client';
 import { createClientSchema, type CreateClientInput } from '@/lib/validators/clients';
 import type { CountryCode } from '@/lib/i18n/countries';
+import { primaryTimezoneFor } from '@/lib/i18n/timezones';
 
 interface ClientFormProps {
   open: boolean;
@@ -84,6 +85,17 @@ export function ClientForm({ open, onOpenChange, client, onUseExistingClient }:
   const { fields, append, remove } = useFieldArray({ control, name: 'contacts' });
   const tagIds = watch('tagIds') ?? [];
 
+  // When the rep picks a country and no timezone is set yet, pre-fill the
+  // timezone with the country's primary IANA zone. Skips when the user has
+  // already chosen a zone explicitly so we never clobber a deliberate pick.
+  const watchedNationality = watch('nationalityIso');
+  const watchedTimezone = watch('timezone');
+  useEffect(() => {
+    if (!watchedNationality || watchedTimezone) return;
+    const primary = primaryTimezoneFor(watchedNationality as CountryCode);
+    if (primary) setValue('timezone', primary);
+  }, [watchedNationality, watchedTimezone, setValue]);
+
   // Populate form when editing
   useEffect(() => {
     if (client && open) {
@@ -287,11 +299,17 @@ export function ClientForm({ open, onOpenChange, client, onUseExistingClient }:
                   </div>
 
                   <div className="col-span-2 space-y-1">
-                    <Label className="text-xs">Label</Label>
+                    <Label className="text-xs">
+                      {watch(`contacts.${index}.channel`) === 'other' ? 'Specify' : 'Label'}
+                    </Label>
                     <Input
                       {...register(`contacts.${index}.label`)}
                       className="h-8"
-                      placeholder="work"
+                      placeholder={
+                        watch(`contacts.${index}.channel`) === 'other'
+                          ? 'e.g. Telegram, Signal'
+                          : 'work'
+                      }
                     />
                   </div>