feat: hybrid photo enhance engine (server sharp + client canvas), denoise

- enhance endpoint accepts JSON params, processes original on disk via sharp pipeline (median, modulate, linear, sharpen, mozjpeg)
- client fallback renders full-size canvas, keeps multipart path
- engine selection setting: auto/server/client, auto falls back to client on error/timeout
- denoise slider (median filter), noise-aware auto mode, preview capped at 1600px

public/js/settings.js

@@ -1,4 +1,4 @@
-const DIRTY_FIELDS = ['spamInterval', 'footerLeft', 'footerRight', 'aiPrompt', 'aiAutoCheck', 'shareShowMessage', 'shareShowDate', 'shareShowNames', 'shareShowPhotos', 'cookieNoticeText', 'photoResolution', 'photoQuality'];
+const DIRTY_FIELDS = ['spamInterval', 'footerLeft', 'footerRight', 'aiPrompt', 'aiAutoCheck', 'shareShowMessage', 'shareShowDate', 'shareShowNames', 'shareShowPhotos', 'cookieNoticeText', 'photoResolution', 'photoQuality', 'photoEngine'];
 const SECTION_IDS = ['sec-system', 'sec-antispam', 'sec-share', 'sec-form', 'sec-ai', 'sec-backup', 'sec-bans'];
 const SPAM_MAX = 10080;
 const BAN_REASONS = {
@@ -157,6 +157,9 @@ async function loadSettings() {
   if (s.photo_capture_resolution) pr.value = s.photo_capture_resolution;
   if (!pr.value) pr.value = '640x480';
   document.getElementById('photoQuality').value = s.photo_capture_quality !== undefined && s.photo_capture_quality !== '' ? s.photo_capture_quality : '0.92';
+  const pe = document.getElementById('photoEngine');
+  pe.value = ['auto', 'server', 'client'].includes(s.photo_enhance_engine) ? s.photo_enhance_engine : 'auto';
+  if (!pe.value) pe.value = 'auto';
   snapshotDirty();
   updateSpamUi();
   loadAiQueue();
@@ -496,6 +499,7 @@ async function saveSettings() {
         cookie_notice_text: document.getElementById('cookieNoticeText').value.trim(),
         photo_capture_resolution: document.getElementById('photoResolution').value,
         photo_capture_quality: String(document.getElementById('photoQuality').value),
+        photo_enhance_engine: document.getElementById('photoEngine').value,
       } })
     });
     if (res.ok) {