feat: add shared @sexy.pivoine.art/types package and fix type safety across frontend/backend

- Create packages/types with shared TypeScript domain model interfaces (User, Video, Model, Article, Comment, Recording, etc.)
- Wire both frontend and backend packages to use @sexy.pivoine.art/types via workspace:*
- Update backend Pothos objectRef types to use shared interfaces instead of inline types
- Update frontend $lib/types.ts to re-export from shared package
- Fix all type errors introduced by more accurate nullable types (avatar/banner as string|null UUIDs, author nullable, events/device_info as object[])
- Add artist_name to comment user select in backend resolver
- Widen utility function signatures (getAssetUrl, getUserInitials, calcReadingTime) to accept null/undefined

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/users/[id]/+page.svelte

@@ -27,7 +27,7 @@
 <Meta
   title={displayName}
   description={data.user.description || `${displayName}'s profile`}
-  image={data.user.avatar ? getAssetUrl(data.user.avatar, "thumbnail") : undefined}
+  image={data.user.avatar ? getAssetUrl(data.user.avatar, "thumbnail") ?? undefined : undefined}
 />
 
 <div class="relative min-h-screen bg-gradient-to-br from-background via-primary/5 to-accent/5">
@@ -91,12 +91,7 @@
               >
             </div>
 
-            {#if data.user.location}
-              <div class="flex items-center gap-2 text-muted-foreground mb-4">
-                <span class="icon-[ri--map-pin-line] w-4 h-4"></span>
-                <span>{data.user.location}</span>
-              </div>
-            {/if}
+
 
             {#if data.user.description}
               <p class="text-muted-foreground mb-4">
@@ -148,7 +143,7 @@
           <div class="grid grid-cols-2 md:grid-cols-4 gap-4 mb-6">
             <div class="text-center p-4 rounded-lg bg-accent/10">
               <div class="text-3xl font-bold text-primary">
-                {Math.round(data.gamification.stats.total_weighted_points)}
+                {Math.round(data.gamification.stats.total_weighted_points ?? 0)}
               </div>
               <div class="text-sm text-muted-foreground mt-1">
                 {$_("gamification.points")}
@@ -188,7 +183,7 @@
                 {$_("gamification.achievements")} ({data.gamification.achievements.length})
               </h3>
               <div class="grid grid-cols-2 md:grid-cols-4 lg:grid-cols-6 gap-3">
-                {#each data.gamification.achievements as achievement (achievement.id)}
+                {#each (data.gamification?.achievements ?? []) as achievement (achievement.id)}
                   <div
                     class="flex flex-col items-center gap-2 p-3 rounded-lg bg-accent/10 border border-border/30 hover:border-primary/50 transition-colors"
                     title={achievement.description}
@@ -199,7 +194,7 @@
                     </span>
                     {#if achievement.date_unlocked}
                       <span class="text-xs text-muted-foreground">
-                        {new Date(achievement.date_unlocked).toLocaleDateString($locale)}
+                        {new Date(achievement.date_unlocked).toLocaleDateString($locale ?? undefined)}
                       </span>
                     {/if}
                   </div>