Fix social_media_post postable_id type to uuid and remove duplicate index

Annotations updated to reflect postable_id changed from bigint to uuid
and removal of duplicate postable index.

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

Author: etewiah

app/models/pwb/social_media_post.rb

@@ -29,13 +29,12 @@ module Pwb
 #  created_at               :datetime         not null
 #  updated_at               :datetime         not null
 #  ai_generation_request_id :bigint
-#  postable_id              :string
+#  postable_id              :uuid
 #  website_id               :bigint           not null
 #
 # Indexes
 #
 #  index_pwb_social_media_posts_on_ai_generation_request_id       (ai_generation_request_id)
-#  index_pwb_social_media_posts_on_postable                       (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_postable_type_and_postable_id  (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_scheduled_at                   (scheduled_at)
 #  index_pwb_social_media_posts_on_status                         (status)

spec/factories/pwb_social_media_posts.rb

@@ -23,13 +23,12 @@
 #  created_at               :datetime         not null
 #  updated_at               :datetime         not null
 #  ai_generation_request_id :bigint
-#  postable_id              :string
+#  postable_id              :uuid
 #  website_id               :bigint           not null
 #
 # Indexes
 #
 #  index_pwb_social_media_posts_on_ai_generation_request_id       (ai_generation_request_id)
-#  index_pwb_social_media_posts_on_postable                       (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_postable_type_and_postable_id  (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_scheduled_at                   (scheduled_at)
 #  index_pwb_social_media_posts_on_status                         (status)

spec/models/pwb/social_media_post_spec.rb

@@ -23,13 +23,12 @@
 #  created_at               :datetime         not null
 #  updated_at               :datetime         not null
 #  ai_generation_request_id :bigint
-#  postable_id              :string
+#  postable_id              :uuid
 #  website_id               :bigint           not null
 #
 # Indexes
 #
 #  index_pwb_social_media_posts_on_ai_generation_request_id       (ai_generation_request_id)
-#  index_pwb_social_media_posts_on_postable                       (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_postable_type_and_postable_id  (postable_type,postable_id)
 #  index_pwb_social_media_posts_on_scheduled_at                   (scheduled_at)
 #  index_pwb_social_media_posts_on_status                         (status)