feat(auth): email verification login and personal access tokens

* feat(auth): add email verification login flow with 401 auto-redirect

Replace the old OAuth-based login with email verification codes:
- Backend: send-code / verify-code endpoints, verification_codes table (migration 009), rate limiting, Resend email service
- Frontend: two-step login UI (email → 6-digit OTP), auth store with sendCode/verifyCode
- SDK: ApiClient gains onUnauthorized callback; 401 responses auto-clear token and redirect to /login
- Fix login button staying disabled due to global isLoading state

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix(auth): add brute-force protection, redirect loop guard, and expired code cleanup

- VerifyCode: increment attempts on wrong code, reject after 5 failed tries (migration 010)
- onUnauthorized: skip redirect if already on /login to prevent infinite loops
- SendCode: best-effort cleanup of expired verification codes older than 1 hour

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat(auth): add master verification code for non-production environments

Allow code "888888" to bypass email verification in non-production
environments to simplify development and testing workflows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat(auth): add personal access tokens for CLI and API authentication

Add full-stack PAT support: users create tokens in Settings, CLI authenticates
via `multica auth login`. Server stores SHA-256 hashes only. Auth middleware
extended to accept both JWTs and PATs (distinguished by `mul_` prefix).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/migrations/009_verification_code.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS verification_code;