feat: fit-contain letterbox + smart queue refill

- Replace center-crop with fit-contain (no photo cropping)
- Letterbox bars filled with adjacent edge average color
- Queue fetches in batches until 50 usable assets
- Auto-refill queue on exhaustion, dedup via shown history
- Filter RAW files from asset selection

Co-authored-by: Cursor <cursoragent@cursor.com>

src/web_server.cpp

@@ -157,6 +157,31 @@ void AppWebServer::setupAPIRoutes() {
             _power->enterDeepSleep();
         });
 
+    // Test Immich connectivity
+    _server.on("/api/test-connection", HTTP_POST,
+        [this](AsyncWebServerRequest* req) {
+            Settings s = _settings->get();
+            Serial.printf("[web] Testing connection to: %s (key: %s...)\n",
+                          s.immich_url.c_str(),
+                          s.immich_key.substring(0, 8).c_str());
+
+            // Reinitialize immich client with current settings
+            _immich->begin(s.immich_url, s.immich_key);
+            auto albums = _immich->fetchAlbums();
+
+            JsonDocument doc;
+            if (!albums.empty()) {
+                doc["ok"] = true;
+                doc["msg"] = String("Connected! Found ") + String(albums.size()) + " albums.";
+            } else {
+                doc["ok"] = false;
+                doc["msg"] = "Failed to connect. Check URL and API key.";
+            }
+            String response;
+            serializeJson(doc, response);
+            req->send(200, "application/json", response);
+        });
+
     _server.on("/api/action/reboot", HTTP_POST,
         [](AsyncWebServerRequest* req) {
             req->send(200, "application/json", "{\"ok\":true,\"msg\":\"Rebooting...\"}");
@@ -259,6 +284,7 @@ void AppWebServer::handleGetSettings(AsyncWebServerRequest* request) {
     doc["meta_pos"] = static_cast<uint8_t>(s.meta_pos);
     doc["led_brightness"] = s.led_brightness;
     doc["immich_url"] = s.immich_url;
+    doc["immich_key"] = s.immich_key;
     doc["albums_json"] = s.albums_json;
 
     String response;