feat: add product concept subtitle to radars

A Radar gains an optional Concept — a short subtitle naming the product
and its typical performances, rendered under the title and wrapping to a
balanced second line when long. Old radars default to an empty Concept
on load.

.oxlintrc.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "./node_modules/oxlint/configuration_schema.json",
+  "plugins": ["typescript", "oxc"],
+  "env": {
+    "browser": true,
+    "es2024": true
+  },
+  "categories": {
+    "correctness": "error"
+  }
+}