Add HTTPS support and a management-token gate for the web UI

ESP32 side can now reach the tools server over HTTPS: the Tools Server
field accepts an https:// address for a TLS-terminating reverse proxy
in front of the server (which still only ever speaks plain HTTP
itself), trusting Cloudflare's Origin CA root (embedded at build time)
since that's the common way to get a real cert on a private origin.
Every URL the device builds -- image fetch, config check, manage-menu
data, the QR codes' own links -- goes through one build_url() helper
that picks the scheme from what's configured.

Also adds an optional MANAGEMENT_TOKEN (docker-compose.yml) that gates
the web UI (/, /api/*) behind a shared secret -- unset by default, so
existing trusted-LAN deployments are unaffected. The same token is
entered once during the ESP32's captive-portal setup and gets baked
into the manage-menu's QR code (?token=...), so scanning it just works;
visiting the page without a valid token shows a plain entry prompt
instead of the config UI, and a valid query-param hit sets a cookie so
the page's own fetch()/<img> calls stay authorized for the rest of the
visit. Device-facing /frame/* endpoints are unaffected -- a separate,
already-documented trust boundary.

server/README.md

@@ -29,7 +29,17 @@ algorithm itself -- it just streams the response straight to the panel.
    populated from the environment; changing them in the UI has no effect
    as long as the env vars are set -- they win on every load.)
 5. On the ESP32's captive portal setup form, set the **Tools Server** field
-   to `<this-machine>:8420`.
+   to `<this-machine>:8420`. This server always speaks plain HTTP itself --
+   for HTTPS, put a TLS-terminating reverse proxy (e.g. nginx) in front of
+   it and enter the proxy's `https://` address instead (see
+   `firmware/README.md`'s HTTPS section for what the ESP32 side needs).
+6. **Optional: set `MANAGEMENT_TOKEN`** in `docker-compose.yml` to gate the
+   web UI behind a shared secret (leave unset to keep it open, the
+   previous default -- fine on a trusted LAN). If set, paste the same
+   value into the ESP32's captive portal setup form's **Access Token**
+   field so the manage-menu's "scan to manage" QR code embeds it
+   automatically (`?token=...`); visiting the page without a valid token
+   in the URL shows a plain token-entry prompt instead of the config UI.
 
 ## Endpoints
 
@@ -106,12 +116,15 @@ algorithm itself -- it just streams the response straight to the panel.
   in sequential or shuffle order per the Order setting. Dragging photos
   in the web UI (or using "Show next") only rearranges what's already in
   that lookahead; it doesn't add or remove photos from the album.
-- `/frame/image`, `/frame/advance`, `/frame/photo-info`, and
-  `/frame/share/{asset_id}` aren't authenticated yet. That's fine on a
-  trusted home LAN for now, but worth revisiting once the ESP32 side is
-  wired up to send a shared device token. `/frame/share` at least is
-  scoped to only ever create a link for a photo this frame is actually
-  showing or has queued, not any Immich asset ID someone might guess.
+- `/frame/image`, `/frame/advance`, `/frame/photo-info`, `/frame/face-labels`,
+  and `/frame/share/{asset_id}` -- the device-facing endpoints -- aren't
+  authenticated. That's fine on a trusted home LAN for now, but worth
+  revisiting if this ever needs to sit somewhere less trusted.
+  `/frame/share` at least is scoped to only ever create a link for a
+  photo this frame is actually showing or has queued, not any Immich
+  asset ID someone might guess. The web UI (`/`, `/api/*`) is separately
+  gated by `MANAGEMENT_TOKEN` if set (see Setup above) -- these are two
+  independent trust boundaries, not one shared mechanism.
 - The 6-color palette RGB values in `app/image_pipeline.py` are
   approximations, not measured values (Waveshare doesn't publish exact
   color primaries for this panel) -- tune them once you can compare a