Fix stale documentation found by a doc-accuracy audit

firmware/README.md's HTTP vs HTTPS section still described the
public-CA-bundle trust approach that was tried and abandoned in favor
of pinning one specific certificate -- rewritten to match what's
actually there. docs/architecture.md was missing the back-photo button
entirely (sequence diagram and boot-flow bullets only covered next) and
still said the system talks "over plain HTTP" despite HTTPS support.
docker-compose.yml.example's MANAGEMENT_TOKEN comment understated its
scope (said "the web UI", omitting that every /frame/* endpoint is
gated too).

server/docker-compose.yml.example

@@ -10,9 +10,11 @@ services:
       - CONFIG_PATH=/data/config.json
       - IMMICH_URL=http://your-immich-host:2283
       - IMMICH_API_KEY=your-immich-api-key-here
-      # Optional: gates the web UI (/, /api/*) behind this shared secret --
-      # leave unset to keep it open on a trusted LAN, same as before. Paste
-      # the same value into the ESP32's captive portal setup form (Access
-      # Token field) so its manage-menu QR code embeds it automatically.
+      # Optional: gates the entire server -- the web UI (/, /api/*) AND
+      # every device-facing /frame/* endpoint -- behind this shared secret.
+      # Leave unset to keep it all open on a trusted LAN, same as before.
+      # Paste the same value into the ESP32's captive portal setup form
+      # (Access Token field) so it's sent on every device request and gets
+      # embedded automatically in the manage-menu/share QR codes.
       - MANAGEMENT_TOKEN=changeme
     restart: unless-stopped