Add floating canvas panels, theme settings, and SVG line-spacing analysis.

Canvas Studio now uses dockable floating panels, app settings/help navigation, and improved SVG export; the backend adds an SVG line-spacing analysis API with SciPy acceleration and new design templates.

backend/service/schemas.py

@@ -100,6 +100,38 @@ class Asset(BaseModel):
     created_at: datetime
 
 
+class LineSpacingAnalysisRequest(BaseModel):
+    percentile: float = Field(default=3, ge=0, le=100)
+    elementWidth: float = Field(gt=0)
+    elementHeight: float = Field(gt=0)
+    sampleStep: float = Field(default=2, gt=0)
+
+
+class LineSpacingClosestPoints(BaseModel):
+    ax: float
+    ay: float
+    bx: float
+    by: float
+
+
+class LineSpacingAnalysisSummary(BaseModel):
+    percentile: float
+    spacingPx: float
+    spacingMm: float
+    minSpacingPx: float
+    minSpacingMm: float
+    sampleStep: float
+    curveCount: int
+    segmentCount: int
+    nearestCount: int
+    sourceWidth: float
+    sourceHeight: float
+    elementWidth: float
+    elementHeight: float
+    computedAt: str
+    closestPoints: LineSpacingClosestPoints | None = None
+
+
 class DesignTemplate(BaseModel):
     template_id: str
     name: str