feat: implement album sharing functionality with permissions management

libertas_api/migrations/20251102161826_create_album_shares_table.sql

@@ -0,0 +1,10 @@
+CREATE TYPE album_permission AS ENUM ('view', 'contribute');
+
+CREATE TABLE album_shares (
+    album_id UUID NOT NULL REFERENCES albums (id) ON DELETE CASCADE,
+    user_id UUID NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    permission album_permission NOT NULL,
+    PRIMARY KEY (album_id, user_id)
+);
+
+CREATE INDEX idx_album_shares_user_id ON album_shares (user_id);