feat(db): Add favicon support and improve remote followers uniqueness constraint

- Add favicon_url column to nodes table for storing node instance favicons
- Replace actor_url unique constraint with composite unique index on (user_id, actor_url) in remote_followers table
- Update database schema and migration files to reflect new constraints
- Improve data integrity by ensuring remote followers are unique per user and actor combination

src/db/schema.ts

@@ -1,4 +1,4 @@
-import { pgTable, text, timestamp, uuid, integer, boolean, index, foreignKey } from 'drizzle-orm/pg-core';
+import { pgTable, text, timestamp, uuid, integer, boolean, index, foreignKey, uniqueIndex } from 'drizzle-orm/pg-core';
 import { relations } from 'drizzle-orm';
 
 // ============================================
@@ -252,7 +252,7 @@ export const remoteFollows = pgTable('remote_follows', {
 export const remoteFollowers = pgTable('remote_followers', {
   id: uuid('id').primaryKey().defaultRandom(),
   userId: uuid('user_id').notNull().references(() => users.id, { onDelete: 'cascade' }), // Local user being followed
-  actorUrl: text('actor_url').notNull().unique(), // Remote actor URL (unique per local user)
+  actorUrl: text('actor_url').notNull(), // Remote actor URL
   inboxUrl: text('inbox_url').notNull(), // Remote user's inbox
   sharedInboxUrl: text('shared_inbox_url'), // Optional shared inbox
   handle: text('handle'), // Remote user's handle (e.g., user@mastodon.social)
@@ -261,6 +261,7 @@ export const remoteFollowers = pgTable('remote_followers', {
 }, (table) => [
   index('remote_followers_user_idx').on(table.userId),
   index('remote_followers_actor_idx').on(table.actorUrl),
+  uniqueIndex('remote_followers_user_actor_unique').on(table.userId, table.actorUrl),
 ]);
 
 // ============================================