feat: use cameleer3-logo.svg from design-system v0.1.36 everywhere

- Sidebar, sign-in page, and favicons all use the single SVG
- Postinstall copies SVG for SaaS HTML favicon (gitignored)
- Sign-in favicon committed (baked into Logto Docker image)
- Remove old PNG favicon references

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

ui/sign-in/src/SignInPage.tsx

@@ -1,6 +1,6 @@
 import { type FormEvent, useMemo, useState } from 'react';
 import { Card, Input, Button, Alert, FormField } from '@cameleer/design-system';
-import cameleerLogo from '@cameleer/design-system/assets/cameleer3-48.png';
+import cameleerLogo from '@cameleer/design-system/assets/cameleer3-logo.svg';
 import { signIn } from './experience-api';
 import styles from './SignInPage.module.css';