fix: eliminate diagonal dither pattern from display driver

Root cause: Panel_ED2208's epd_quality mode applies _dither_row_rgb_pair
(diagonal bias pattern with dither=140) during _exec_transfer(). Since our
ImagePipeline already does proper Floyd-Steinberg dithering, the driver's
additional dithering was creating visible diagonal artifacts.

Fix: setEpdMode(epd_fastest) selects _dither_row_none (clean nearest-color
lookup, no spatial bias). On Panel_ED2208 this only affects the dither
function — NOT refresh quality or waveform.

Also: default dither_noise setting to OFF since error scatter was targeting
the wrong layer (it made gradient areas fuzzier without fixing the real
problem in the display driver).

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

src/immich_client.cpp

@@ -138,6 +138,51 @@ std::vector<String> ImmichClient::fetchRandomAssetIds(int count) {
     return ids;
 }
 
+std::vector<RandomAsset> ImmichClient::fetchRandomAssets(int count) {
+    std::vector<RandomAsset> assets;
+    String url = buildUrl("/api/search/random");
+
+    JsonDocument reqDoc;
+    reqDoc["size"] = count;
+    reqDoc["type"] = "IMAGE";
+    String body;
+    serializeJson(reqDoc, body);
+
+    String response = httpPost(url, body);
+    if (response.isEmpty()) return assets;
+
+    JsonDocument doc;
+    DeserializationError err = deserializeJson(doc, response);
+    if (err) return assets;
+
+    JsonArray arr = doc.as<JsonArray>();
+    int skippedRaw = 0;
+    for (JsonObject asset : arr) {
+        String id = asset["id"].as<String>();
+        if (id.length() == 0) continue;
+
+        String filename = asset["originalFileName"] | "";
+        filename.toLowerCase();
+        if (filename.endsWith(".dng") || filename.endsWith(".raw") ||
+            filename.endsWith(".cr2") || filename.endsWith(".cr3") ||
+            filename.endsWith(".nef") || filename.endsWith(".arw") ||
+            filename.endsWith(".orf") || filename.endsWith(".rw2") ||
+            filename.endsWith(".raf") || filename.endsWith(".srw")) {
+            skippedRaw++;
+            continue;
+        }
+
+        RandomAsset ra;
+        ra.id = id;
+        ra.dateTime = asset["localDateTime"] | "";
+        assets.push_back(ra);
+    }
+
+    Serial.printf("[immich] Fetched %d random assets with dates (skipped %d RAW)\n",
+                  assets.size(), skippedRaw);
+    return assets;
+}
+
 std::vector<String> ImmichClient::fetchFavoriteAssetIds() {
     std::vector<String> ids;
     String url = buildUrl("/api/assets?isFavorite=true");