Implement Passkey registration

- Create Identity credentials
- Add management UI and registration flow

db/migrate/20260213154740_create_identity_credentials.rb

@@ -0,0 +1,17 @@
+class CreateIdentityCredentials < ActiveRecord::Migration[8.2]
+  def change
+    create_table :identity_credentials, id: :uuid do |t|
+      t.uuid :identity_id, null: false
+      t.string :credential_id, null: false
+      t.binary :public_key, null: false
+      t.integer :sign_count, null: false, default: 0
+      t.string :name
+      t.text :transports
+
+      t.timestamps
+
+      t.index :identity_id
+      t.index :credential_id, unique: true
+    end
+  end
+end

db/schema.rb

@@ -344,6 +344,19 @@ ActiveRecord::Schema[8.2].define(version: 2026_02_18_120000) do
     t.index ["identity_id"], name: "index_access_token_on_identity_id"
   end
 
+  create_table "identity_credentials", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.datetime "created_at", null: false
+    t.string "credential_id", null: false
+    t.uuid "identity_id", null: false
+    t.string "name"
+    t.binary "public_key", null: false
+    t.integer "sign_count", default: 0, null: false
+    t.text "transports"
+    t.datetime "updated_at", null: false
+    t.index ["credential_id"], name: "index_identity_credentials_on_credential_id", unique: true
+    t.index ["identity_id"], name: "index_identity_credentials_on_identity_id"
+  end
+
   create_table "magic_links", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "code", null: false
     t.datetime "created_at", null: false