Render mermaid diagram per risk assessment scope

Each scope card now shows a flowchart of its nodes, processes, and
threats, with a distinct shape per type: stadium for entities,
hexagon for boundaries, rectangle for assets, cylinder for data, and
a red hexagon for threats attached via dashed edges to their process
target. The Mermaid source is built on the backend and exposed as a
new `mermaid` field on RiskAssessmentScope; the frontend just renders
it via @probo/ui's MermaidDiagram and shows a copy button + legend.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/server/api/console/v1/graphql/risk_assessment.graphql

@@ -228,6 +228,8 @@ type RiskAssessmentScope implements Node {
         orderBy: RiskAssessmentScenarioOrder
     ): RiskAssessmentScenarioConnection @goField(forceResolver: true)
 
+    mermaidChart: String! @goField(forceResolver: true)
+
     createdAt: Datetime!
     updatedAt: Datetime!
 }