feat: add api_input LED interpolation; fix LED preview, FPS charts, dashboard layout

API Input:
- Add interpolation mode (linear/nearest/none) for LED count mismatch
  between incoming data and device LED count
- New IconSelect in editor, i18n for en/ru/zh
- Mark crossfade as won't-do (client owns temporal transitions)
- Mark last-write-wins as already implemented

LED Preview:
- Fix zone-mode preview parsing composite wire format (0xFE header
  bytes were rendered as color data, garbling multi-zone previews)
- Fix _restoreLedPreviewState to handle zone-mode panels

FPS Charts:
- Seed target card charts from server metrics-history on first load
- Add fetchMetricsHistory() with 5s TTL cache shared across
  dashboard, targets, perf-charts, and graph-editor
- Fix chart padding: pass maxSamples per caller (120 for dashboard,
  30 for target cards) instead of hardcoded 120
- Fix dashboard chart empty on tab switch (always fetch server history)
- Left-pad with nulls for consistent chart width across targets

Dashboard:
- Fix metrics row alignment (grid layout with fixed column widths)
- Fix FPS label overflow into uptime column

server/src/wled_controller/api/schemas/color_strip_sources.py

@@ -93,6 +93,7 @@ class ColorStripSourceCreate(BaseModel):
     # api_input-type fields
     fallback_color: Optional[List[int]] = Field(None, description="Fallback RGB color [R,G,B] when no data received (api_input type)")
     timeout: Optional[float] = Field(None, description="Seconds before reverting to fallback (api_input type)", ge=0.0, le=300.0)
+    interpolation: Optional[str] = Field(None, description="LED count interpolation mode: none|linear|nearest (api_input type)")
     # notification-type fields
     notification_effect: Optional[str] = Field(None, description="Notification effect: flash|pulse|sweep")
     duration_ms: Optional[int] = Field(None, ge=100, le=10000, description="Effect duration in milliseconds")
@@ -163,6 +164,7 @@ class ColorStripSourceUpdate(BaseModel):
     # api_input-type fields
     fallback_color: Optional[List[int]] = Field(None, description="Fallback RGB color [R,G,B] (api_input type)")
     timeout: Optional[float] = Field(None, description="Timeout before fallback (api_input type)", ge=0.0, le=300.0)
+    interpolation: Optional[str] = Field(None, description="LED count interpolation mode: none|linear|nearest (api_input type)")
     # notification-type fields
     notification_effect: Optional[str] = Field(None, description="Notification effect: flash|pulse|sweep")
     duration_ms: Optional[int] = Field(None, ge=100, le=10000, description="Effect duration in milliseconds")
@@ -234,6 +236,7 @@ class ColorStripSourceResponse(BaseModel):
     # api_input-type fields
     fallback_color: Optional[List[int]] = Field(None, description="Fallback RGB color [R,G,B] (api_input type)")
     timeout: Optional[float] = Field(None, description="Timeout before fallback (api_input type)")
+    interpolation: Optional[str] = Field(None, description="LED count interpolation mode: none|linear|nearest (api_input type)")
     # notification-type fields
     notification_effect: Optional[str] = Field(None, description="Notification effect: flash|pulse|sweep")
     duration_ms: Optional[int] = Field(None, description="Effect duration in milliseconds")