security: round 3 — token security (crypto random, hashed storage, portal middleware)

Token generation:
- Replace Str::ulid() with bin2hex(random_bytes(32)) for 256-bit entropy
- Store SHA-256 hash in database, never plaintext tokens
- Hash input before lookup on all token endpoints

Invitation tokens:
- InvitationService: generate crypto random, store hash, pass plain
  token transiently for email URL via UserInvitation::$plainToken
- InvitationController show/accept: hash input before DB lookup
- AcceptInvitationRequest: hash token before invitation lookup
- Migration: widen user_invitations.token and artists.portal_token
  from char(26) to char(64) for SHA-256 hex digests

Portal token auth:
- PortalTokenController: remove Schema::hasTable() runtime checks,
  hash token before lookup, return shaped response via PortalEventResource
  instead of raw model data
- Create PortalEventResource (name, dates, status only — no internals)
- Handle missing production_requests table gracefully via try/catch

Portal token middleware:
- Implement full token validation: extract from Bearer header or ?token=
  query param, hash, look up in artists/production_requests, verify
  event exists and is not draft/closed, set portal context on request
- Return generic 401 on any failure (no information leakage)

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

api/app/Models/UserInvitation.php

@@ -15,6 +15,12 @@ final class UserInvitation extends Model
     use HasFactory;
     use HasUlids;
 
+    /**
+     * Plain-text token, set transiently after creation for use in emails.
+     * Never persisted — the DB stores only the SHA-256 hash.
+     */
+    public ?string $plainToken = null;
+
     protected $fillable = [
         'email',
         'event_id',