feat(displays): expose DDC/CI contrast, input source, color preset, picture mode

Backend (routes/display.py, services/display_service.py):
- Probe DDC/CI capabilities per monitor at enumeration time
- New endpoints POST /api/display/{contrast,input_source,color_preset,picture_mode}/{id}
- Picture mode goes through raw VCP 0xDC since monitorcontrol has no
  high-level wrapper; labels follow MCCS spec with vendor-friendly fallbacks
- Each capability reports a *_supported flag so the UI can hide rows that
  the hardware does not advertise

Frontend (links.js, app.js, styles.css, locales):
- Monitor cards grow a contrast slider (same editorial copper treatment
  as brightness) and a "PICTURE TUNING" section beneath
- Picture tuning uses the IconSelect widget (matching the audio device
  selector): per-port icons (HDMI, DisplayPort, DVI, VGA, USB-C),
  thermometer for color temps, per-mode icons (movie reel, gamepad,
  ball, etc.) for picture modes
- Humanizers turn SHOUT_CASE enum names into readable labels
  (COLOR_TEMP_6500K -> "6500 K", HDMI1 -> "HDMI 1")
- 14 new i18n keys per locale (en/ru)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

media_server/static/js/app.js

@@ -63,6 +63,8 @@ import {
 
 import {
     loadDisplayMonitors, onDisplayBrightnessInput, onDisplayBrightnessChange,
+    onDisplayContrastInput, onDisplayContrastChange,
+    onDisplayInputSourceChange, onDisplayColorPresetChange, onDisplayPictureModeChange,
     toggleDisplayPower, loadHeaderLinks, loadLinksTable,
     showAddLinkDialog, showEditLinkDialog, closeLinkDialog, saveLink, deleteLinkConfirm,
     linkFormDirty, setLinkFormDirty,
@@ -127,6 +129,8 @@ Object.assign(window, {
     saveLink, deleteLinkConfirm,
     // Display
     loadDisplayMonitors, onDisplayBrightnessInput, onDisplayBrightnessChange,
+    onDisplayContrastInput, onDisplayContrastChange,
+    onDisplayInputSourceChange, onDisplayColorPresetChange, onDisplayPictureModeChange,
     toggleDisplayPower,
     // Audio device
     onAudioDeviceChanged,