fix(mermaid): escape special characters in node labels

Fixes issue #21: parentheses and other special characters in node names
now break Mermaid rendering on GitHub.

Added escapeMermaidLabel() helper that wraps labels in double quotes
when they contain Mermaid shape delimiters or special characters:
( ) { } [ ] / \

This allows nodes like "Firebase Hosting (Tenant UI)" to render correctly
in all generated Mermaid diagrams. The quoted labels are properly
interpreted by Mermaid parsers as literal text.

Fixes #21

Author: Mearman

src/operations/graph-shared.ts

@@ -145,6 +145,25 @@ export function mermaidShapeForNode(node: Node): MermaidShape {
 	return NODE_TYPE_SHAPES[node.type] ?? "rectangle";
 }
 
+/**
+ * Escape a Mermaid label by wrapping in quotes if it contains special characters.
+ * Mermaid shape delimiters and other special chars need escaping: ( ) { } [ ] / \
+ * Wrapping in double quotes allows these characters to be rendered as-is.
+ * @param label - The label text to escape
+ * @returns The label, quoted if it contains special characters
+ * @example
+ * escapeMermaidLabel("Firebase (Tenant)") // returns '"Firebase (Tenant)"'
+ */
+function escapeMermaidLabel(label: string): string {
+	// Check if label contains any Mermaid special characters that need escaping
+	const specialChars = ["(", ")", "{", "}", "[", "]", "/", "\\"];
+	if (specialChars.some((char) => label.includes(char))) {
+		// Wrap in double quotes to escape
+		return `"${label}"`;
+	}
+	return label;
+}
+
 /**
  * Render a Mermaid node definition for a node id/name/shape.
  * @param id - Node id
@@ -161,16 +180,17 @@ export function renderMermaidNode(
 ): string {
 	const safeId = sanitiseMermaidId(id);
 	const label = mode === "compact" ? id : `${id}: ${name}`;
+	const escapedLabel = escapeMermaidLabel(label);
 	switch (shape) {
 		case "rounded":
-			return `${safeId}([${label}])`;
+			return `${safeId}([${escapedLabel}])`;
 		case "rhombus":
-			return `${safeId}{{${label}}}`;
+			return `${safeId}{{${escapedLabel}}}`;
 		case "parallelogram":
-			return `${safeId}[/${label}/]`;
+			return `${safeId}[/${escapedLabel}/]`;
 		case "rectangle":
 		default:
-			return `${safeId}[${label}]`;
+			return `${safeId}[${escapedLabel}]`;
 	}
 }