Security hardening: env-based config, CSRF protection, secure code generation, plus presenter management and email communications system

- Move all credentials from hardcoded to .env with python-dotenv (add .env.example template and .gitignore)
- Add CSRF token generation and validation on all state-changing requests
- Replace random.choices with secrets.choice for all secure code generation
- Add session cookie security headers (HttpOnly, Secure, SameSite)
- Add presenter management: assign/remove presenters to breakout sessions, presenter QR scanning
- Add email communications system: templates per event, custom email sending, sent email tracking
- Add staff/organizer profile pages with staff code display
- New DB tables: event_email_templates, sent_emails, user_communications
- New DB columns: staff.reminder_count/reminder_dates, breakout_session_organizers.presenter_code
- Expand English translation strings across all new features

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

static/favicon.svg

@@ -1,9 +1,13 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
-  <rect width="32" height="32" rx="6" fill="#1a1a2e"/>
-  <text x="16" y="22" font-family="Arial, sans-serif" font-size="14" font-weight="700" fill="#ffffff" text-anchor="middle">NE</text>
-  <circle cx="6" cy="10" r="2" fill="#3b82f6"/>
-  <circle cx="26" cy="10" r="2" fill="#3b82f6"/>
-  <circle cx="16" cy="6" r="2" fill="#3b82f6"/>
-  <line x1="6" y1="10" x2="16" y2="6" stroke="#3b82f6" stroke-width="1.5"/>
-  <line x1="26" y1="10" x2="16" y2="6" stroke="#3b82f6" stroke-width="1.5"/>
-</svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32" fill="none">
+  <!-- Hexagon background -->
+  <polygon points="16,1 29,8 29,23 16,30 3,23 3,8" fill="#1e3a5f"/>
+  <!-- 4 dots in a square -->
+  <circle cx="10" cy="10" r="2.5" fill="#ffffff" opacity="0.9"/>
+  <circle cx="22" cy="10" r="2.5" fill="#ffffff" opacity="0.9"/>
+  <circle cx="22" cy="21" r="2.5" fill="#ffffff" opacity="0.9"/>
+  <circle cx="10" cy="21" r="2.5" fill="#ffffff" opacity="0.9"/>
+  <!-- N-pattern: BL->TL, TL->BR, BR->TR -->
+  <line x1="10" y1="21" x2="10" y2="10" stroke="#ffffff" stroke-width="1.5" opacity="0.7"/>
+  <line x1="10" y1="10" x2="22" y2="21" stroke="#ffffff" stroke-width="1.5" opacity="0.7"/>
+  <line x1="22" y1="21" x2="22" y2="10" stroke="#ffffff" stroke-width="1.5" opacity="0.7"/>
+</svg>