feat(server/auth): switch user identity to phone with email optional

Phone becomes the required, unique login identifier; email and name turn
optional. Login now accepts either via a single identifier field, refresh
re-checks tenant membership, and the dev seed provides phone numbers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/migrations/20260428120000_prepare_user_phone_identity.down.sql

@@ -0,0 +1,24 @@
+DROP INDEX IF EXISTS idx_users_name_trgm_active;
+DROP INDEX IF EXISTS idx_users_phone_trgm_active;
+DROP INDEX IF EXISTS idx_users_email_trgm_active;
+DROP INDEX IF EXISTS idx_users_status_created_at;
+DROP INDEX IF EXISTS uk_users_phone_active;
+
+UPDATE users
+SET email = 'user-' || id || '@rollback.local'
+WHERE email IS NULL;
+
+UPDATE users
+SET name = COALESCE(NULLIF(phone, ''), email, 'user-' || id)
+WHERE name IS NULL;
+
+ALTER TABLE users
+    ALTER COLUMN email SET NOT NULL,
+    ALTER COLUMN phone DROP NOT NULL,
+    ALTER COLUMN name SET NOT NULL;
+
+DROP INDEX IF EXISTS uk_users_email_active;
+
+CREATE UNIQUE INDEX uk_users_email_active
+    ON users(email)
+    WHERE deleted_at IS NULL;