feat(help): public /help setup-and-troubleshooting page

Anchor for the manual QR baked into the firmware Step 1/2 screen
(pictureframe-firmware e089911). One self-contained Twig page,
PUBLIC_ACCESS in security.yaml, /help excluded from the SPA catch-all
regex so it doesn't get swallowed.

Scope is deliberately tight: first-time setup screen by screen, the
captive-portal-didn't-open fallback (manual nav to 192.168.4.1 plus
the iOS lock-screen-scan caveat), the connection-failed retry path,
how to wipe the frame for a new account, photo-not-appearing
diagnosis, and what the yellow/red status borders mean. Anything
beyond that goes in the SPA proper, not here.

No frontend rebuild needed — pure server-rendered Twig + inline CSS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

config/packages/security.yaml

@@ -36,6 +36,7 @@ security:
         - { path: ^/register, roles: PUBLIC_ACCESS }
         - { path: ^/setup, roles: PUBLIC_ACCESS }
         - { path: ^/token, roles: PUBLIC_ACCESS }
+        - { path: ^/help, roles: PUBLIC_ACCESS }
         - { path: ^/api/device, roles: PUBLIC_ACCESS }
         - { path: ^/, roles: ROLE_USER }