Add Pattern Templates for Key Colors targets with visual canvas editor

Introduce Pattern Template entity as a reusable rectangle layout that
Key Colors targets reference via pattern_template_id. This replaces
inline rectangle storage with a shared template system.

Backend:
- New PatternTemplate data model, store (JSON persistence), CRUD API
- KC targets now reference pattern_template_id instead of inline rectangles
- ProcessorManager resolves pattern template at KC processing start
- Picture source test endpoint supports capture_duration=0 for single frame
- Delete protection: 409 when template is referenced by a KC target

Frontend:
- Pattern Templates section in Key Colors sub-tab with card UI
- Visual canvas editor with drag-to-move, 8-point resize handles
- Background capture from any picture source for visual alignment
- Precise coordinate list synced bidirectionally with canvas
- Resizable editor container, viewport-constrained modal
- KC target editor uses pattern template dropdown instead of inline rects
- Localization (en/ru) for all new UI elements

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

server/src/wled_controller/static/style.css

@@ -2706,3 +2706,157 @@ input:-webkit-autofill:focus {
     padding: 4px 0;
 }
 
+/* Pattern Template Visual Editor */
+.modal-content-wide {
+    max-width: 900px !important;
+    width: 95% !important;
+    max-height: calc(100vh - 40px);
+    display: flex;
+    flex-direction: column;
+}
+
+.modal-content-wide .modal-body {
+    overflow-y: auto;
+    flex: 1 1 auto;
+    min-height: 0;
+}
+
+.pattern-canvas-container {
+    position: relative;
+    border-radius: 8px;
+    overflow: hidden;
+    background: var(--bg-color);
+    border: 1px solid var(--border-color);
+    margin-bottom: 12px;
+    resize: vertical;
+    min-height: 200px;
+    height: 450px;
+    max-height: calc(100vh - 400px);
+}
+
+#pattern-canvas {
+    width: 100%;
+    height: 100%;
+    display: block;
+    cursor: crosshair;
+}
+
+.pattern-canvas-toolbar {
+    display: flex;
+    gap: 0.5rem;
+    padding: 8px 0;
+    align-items: center;
+}
+
+.pattern-canvas-toolbar .btn {
+    flex: 0 0 auto;
+    min-width: auto;
+    padding: 6px 12px;
+    font-size: 0.85rem;
+}
+
+.pattern-bg-row {
+    display: flex;
+    gap: 0.5rem;
+    align-items: center;
+    margin-bottom: 8px;
+}
+
+.pattern-bg-row select {
+    flex: 1;
+}
+
+.pattern-capture-btn {
+    flex: 0 0 auto;
+    min-width: 36px !important;
+    width: 36px;
+    height: 36px;
+    padding: 0 !important;
+    font-size: 1.1rem;
+    line-height: 36px;
+    text-align: center;
+}
+
+.pattern-rect-list {
+    display: flex;
+    flex-direction: column;
+    gap: 6px;
+    margin-top: 8px;
+    max-height: 200px;
+    overflow-y: auto;
+}
+
+.pattern-rect-row {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 6px 8px;
+    background: var(--bg-color);
+    border: 1px solid var(--border-color);
+    border-radius: 6px;
+    font-size: 0.85rem;
+    cursor: pointer;
+    transition: border-color 0.15s;
+}
+
+.pattern-rect-row.selected {
+    border-color: var(--primary-color);
+    background: rgba(76, 175, 80, 0.08);
+}
+
+.pattern-rect-row input[type="text"] {
+    flex: 2;
+    min-width: 0;
+    padding: 4px 6px;
+    font-size: 0.8rem;
+}
+
+.pattern-rect-row input[type="number"] {
+    flex: 1;
+    min-width: 0;
+    width: 55px;
+    padding: 4px 6px;
+    font-size: 0.8rem;
+}
+
+.pattern-rect-row .pattern-rect-remove-btn {
+    background: none;
+    border: none;
+    color: #777;
+    font-size: 0.9rem;
+    cursor: pointer;
+    padding: 2px 4px;
+    border-radius: 4px;
+    flex-shrink: 0;
+    transition: color 0.2s, background 0.2s;
+}
+
+.pattern-rect-row .pattern-rect-remove-btn:hover {
+    color: var(--danger-color);
+    background: rgba(244, 67, 54, 0.1);
+}
+
+.pattern-rect-labels {
+    display: flex;
+    gap: 6px;
+    padding: 0 8px;
+    margin-bottom: 2px;
+    font-size: 0.7rem;
+    color: var(--text-secondary);
+    font-weight: 600;
+}
+
+.pattern-rect-labels span:first-child {
+    flex: 2;
+}
+
+.pattern-rect-labels span {
+    flex: 1;
+    text-align: center;
+}
+
+.pattern-rect-labels span:last-child {
+    width: 24px;
+    flex: 0 0 24px;
+}
+