Introduce Picture Targets to separate processing from devices

Add PictureTarget entity that bridges PictureSource to output device,
separating processing settings from device connection/calibration state.
This enables future target types (Art-Net, E1.31) and cleanly decouples
"what to stream" from "where to stream."

- Add PictureTarget/WledPictureTarget dataclasses and storage
- Split ProcessorManager into DeviceState (health) + TargetState (processing)
- Add /api/v1/picture-targets endpoints (CRUD, start/stop, settings, metrics)
- Simplify device API (remove processing/settings/metrics endpoints)
- Auto-migrate existing device settings to picture targets on first startup
- Add Targets tab to WebUI with target cards and editor modal
- Add en/ru locale keys for targets UI

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/style.css

@@ -387,9 +387,11 @@ section {
 
 .card-actions {
     display: flex;
-    flex-wrap: wrap;
-    gap: 10px;
-    justify-content: center;
+    gap: 8px;
+    margin-top: auto;
+    padding-top: 12px;
+    border-top: 1px solid var(--border-color);
+    align-items: center;
 }
 
 .btn {
@@ -2534,9 +2536,7 @@ input:-webkit-autofill:focus {
 }
 
 .stream-card-prop {
-    display: inline-flex;
-    align-items: center;
-    gap: 3px;
+    display: inline-block;
     font-size: 0.75rem;
     color: var(--text-secondary);
     background: var(--border-color);
@@ -2546,6 +2546,7 @@ input:-webkit-autofill:focus {
     overflow: hidden;
     text-overflow: ellipsis;
     max-width: 180px;
+    vertical-align: middle;
 }
 
 .stream-card-prop-full {