Add Key Colors target type for extracting colors from screen regions

Introduce a new "key_colors" target type alongside WLED targets, enabling
real-time color extraction from configurable screen rectangles with
average/median/dominant modes, temporal smoothing, and WebSocket streaming.

- Split WledPictureTarget into its own module, add KeyColorsPictureTarget
- Add KC target lifecycle to ProcessorManager (register, start/stop, processing loop)
- Extend API routes and schemas for KC targets (CRUD, settings, state, metrics, colors)
- Add WebSocket endpoint for real-time color updates with auth
- Add KC sub-tab in Targets UI with editor modal and live color swatches
- Add EN and RU translations for all key colors strings

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

server/src/wled_controller/static/style.css

@@ -2583,3 +2583,126 @@ input:-webkit-autofill:focus {
     font-size: 0.7rem;
 }
 
+/* Key Colors target styles */
+.kc-rect-list {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+    margin-bottom: 8px;
+}
+
+.kc-rect-row {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 8px;
+    background: var(--bg-color);
+    border: 1px solid var(--border-color);
+    border-radius: 6px;
+}
+
+.kc-rect-row input[type="text"] {
+    flex: 2;
+    min-width: 0;
+}
+
+.kc-rect-row input[type="number"] {
+    flex: 1;
+    min-width: 0;
+    width: 60px;
+}
+
+.kc-rect-row .kc-rect-remove-btn {
+    background: none;
+    border: none;
+    color: #777;
+    font-size: 1rem;
+    cursor: pointer;
+    padding: 4px;
+    border-radius: 4px;
+    flex-shrink: 0;
+    transition: color 0.2s, background 0.2s;
+}
+
+.kc-rect-row .kc-rect-remove-btn:hover {
+    color: var(--danger-color);
+    background: rgba(244, 67, 54, 0.1);
+}
+
+.kc-rect-labels {
+    display: flex;
+    gap: 6px;
+    padding: 0 8px;
+    margin-bottom: 4px;
+    font-size: 0.7rem;
+    color: var(--text-secondary);
+    font-weight: 600;
+}
+
+.kc-rect-labels span:first-child {
+    flex: 2;
+}
+
+.kc-rect-labels span {
+    flex: 1;
+    text-align: center;
+}
+
+.kc-rect-labels span:last-child {
+    width: 28px;
+    flex: 0 0 28px;
+}
+
+.kc-add-rect-btn {
+    width: 100%;
+    font-size: 0.85rem;
+    padding: 6px 12px;
+}
+
+.kc-rect-empty {
+    text-align: center;
+    color: var(--text-secondary);
+    font-size: 0.85rem;
+    padding: 12px;
+    font-style: italic;
+}
+
+.kc-color-swatches {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 6px;
+    margin-bottom: 8px;
+}
+
+.kc-swatch {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 3px;
+}
+
+.kc-swatch-color {
+    width: 32px;
+    height: 32px;
+    border-radius: 6px;
+    border: 2px solid var(--border-color);
+    transition: background-color 0.3s;
+}
+
+.kc-swatch-label {
+    font-size: 0.6rem;
+    color: var(--text-secondary);
+    max-width: 40px;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    text-align: center;
+}
+
+.kc-no-colors {
+    color: var(--text-secondary);
+    font-size: 0.8rem;
+    font-style: italic;
+    padding: 4px 0;
+}
+