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.up.sql

@@ -0,0 +1,36 @@
+CREATE EXTENSION IF NOT EXISTS pg_trgm;
+
+UPDATE users
+SET phone = '0' || LPAD(id::text, 19, '0')
+WHERE phone IS NULL;
+
+ALTER TABLE users
+    ALTER COLUMN email DROP NOT NULL,
+    ALTER COLUMN phone SET NOT NULL,
+    ALTER COLUMN name DROP NOT NULL;
+
+DROP INDEX IF EXISTS uk_users_email_active;
+
+CREATE UNIQUE INDEX uk_users_email_active
+    ON users(email)
+    WHERE email IS NOT NULL AND deleted_at IS NULL;
+
+CREATE UNIQUE INDEX IF NOT EXISTS uk_users_phone_active
+    ON users(phone)
+    WHERE deleted_at IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_users_status_created_at
+    ON users(status, created_at DESC)
+    WHERE deleted_at IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_users_email_trgm_active
+    ON users USING GIN (email gin_trgm_ops)
+    WHERE email IS NOT NULL AND deleted_at IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_users_phone_trgm_active
+    ON users USING GIN (phone gin_trgm_ops)
+    WHERE deleted_at IS NULL;
+
+CREATE INDEX IF NOT EXISTS idx_users_name_trgm_active
+    ON users USING GIN (name gin_trgm_ops)
+    WHERE name IS NOT NULL AND deleted_at IS NULL;