Add ExpertiseSelect component for onboarding

Replace database-backed TagInput with a cleaner ExpertiseSelect
component that has predefined ocean conservation expertise areas.
Features a checkbox grid UI that's more user-friendly for onboarding.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/(auth)/onboarding/page.tsx

@@ -22,7 +22,7 @@ import {
   SelectValue,
 } from '@/components/ui/select'
 import { toast } from 'sonner'
-import { TagInput } from '@/components/shared/tag-input'
+import { ExpertiseSelect } from '@/components/shared/expertise-select'
 import {
   User,
   Phone,
@@ -202,15 +202,11 @@ export default function OnboardingPage() {
               </CardDescription>
             </CardHeader>
             <CardContent className="space-y-4">
-              <div className="space-y-2">
-                <Label>Expertise Tags</Label>
-                <TagInput
-                  value={expertiseTags}
-                  onChange={setExpertiseTags}
-                  placeholder="Select your expertise areas..."
-                  maxTags={10}
-                />
-              </div>
+              <ExpertiseSelect
+                value={expertiseTags}
+                onChange={setExpertiseTags}
+                maxTags={5}
+              />
 
               <div className="flex gap-2">
                 <Button variant="outline" onClick={goBack} className="flex-1">