feat(api): add tags to resource creation

Normalize tag names before attaching them, reject names that are too short
after sanitization, and return 404 when removing tags not attached to the
resource.

Adds a per-team unique tag-name index and migrates duplicate tags onto the
kept record before creating the constraint.

app/Models/Tag.php

@@ -3,6 +3,7 @@
 namespace App\Models;
 
 use App\Traits\HasSafeStringAttribute;
+use Illuminate\Support\Facades\DB;
 use OpenApi\Attributes as OA;
 
 #[OA\Schema(
@@ -34,6 +35,13 @@ class Tag extends BaseModel
         return Tag::whereTeamId(currentTeam()->id)->orderBy('name');
     }
 
+    public function deleteIfOrphaned(): void
+    {
+        if (DB::table('taggables')->where('tag_id', $this->id)->doesntExist()) {
+            $this->delete();
+        }
+    }
+
     public function applications()
     {
         return $this->morphedByMany(Application::class, 'taggable');