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.

CONTEXT.md

@@ -24,6 +24,11 @@ A single integer in **{0, 1, 2, 3, 4, 5}** assigned to one (Criterion, Profile)
 
 - **Aliases to avoid:** *note* (French calque — use *Score*), *rating* (acceptable in user-facing copy, but *Score* is canonical in code).
 
+### Concept
+A short free-text subtitle on a Radar that names the product and helps the reader identify its typical performances at a glance. Optional — a Radar may have an empty Concept. Rendered under the Radar name (the title) on the chart, wrapping to a second line when long.
+
+- **Aliases to avoid:** *subtitle* (that's the visual role, not the domain term), *description* (too generic — a Concept is a tight positioning phrase, not prose), *tagline* (acceptable in user-facing copy, but *Concept* is canonical in code).
+
 ## Conventions
 
 ### Higher is better

src/components/RadarChart.vue

@@ -14,7 +14,47 @@ const props = withDefaults(
 
 const WIDTH = 720
 const HEIGHT = computed(() => (props.withChrome === false ? 600 : 800))
-const TITLE_H = computed(() => (props.withChrome === false ? 0 : 60))
+
+const subtitleText = computed(() => props.radar.concept?.trim() ?? '')
+
+const SUBTITLE_SINGLE_LINE_MAX = 64
+
+function wrapToTwoLines(text: string): string[] {
+  const words = text.split(/\s+/).filter(Boolean)
+  if (words.length < 2) return [text]
+  let bestSplit = 1
+  let bestDiff = Infinity
+  for (let i = 1; i < words.length; i++) {
+    const diff = Math.abs(
+      words.slice(0, i).join(' ').length - words.slice(i).join(' ').length,
+    )
+    if (diff < bestDiff) {
+      bestDiff = diff
+      bestSplit = i
+    }
+  }
+  return [words.slice(0, bestSplit).join(' '), words.slice(bestSplit).join(' ')]
+}
+
+// 0 lines = no concept, 1 = fits, 2 = wrapped.
+const subtitleLines = computed<string[]>(() => {
+  const text = subtitleText.value
+  if (props.withChrome === false || !text) return []
+  return text.length <= SUBTITLE_SINGLE_LINE_MAX ? [text] : wrapToTwoLines(text)
+})
+
+const TITLE_H = computed(() => {
+  if (props.withChrome === false) return 0
+  const n = subtitleLines.value.length
+  return n === 0 ? 60 : n === 1 ? 92 : 116
+})
+
+const titleY = computed(() =>
+  subtitleLines.value.length === 0 ? TITLE_H.value / 2 + 4 : 32,
+)
+const subtitleFontSize = computed(() => (subtitleLines.value.length > 1 ? 14 : 16))
+const subtitleStartY = computed(() => (subtitleLines.value.length > 1 ? 56 : 64))
+const subtitleLineHeight = computed(() => (subtitleLines.value.length > 1 ? 18 : 0))
 const LEGEND_H = computed(() => (props.withChrome === false ? 0 : 120))
 const CHART_TOP = computed(() => TITLE_H.value)
 const CHART_BOTTOM = computed(() => HEIGHT.value - LEGEND_H.value)
@@ -140,7 +180,7 @@ const insufficientCriteria = computed(() => props.radar.criteria.length < 3)
     <text
       v-if="withChrome !== false"
       :x="WIDTH / 2"
-      :y="TITLE_H / 2 + 4"
+      :y="titleY"
       text-anchor="middle"
       dominant-baseline="middle"
       font-size="28"
@@ -150,6 +190,20 @@ const insufficientCriteria = computed(() => props.radar.criteria.length < 3)
       {{ titleText }}
     </text>
 
+    <!-- Concept (subtitle, wraps to two lines when long) -->
+    <text
+      v-for="(line, i) in subtitleLines"
+      :key="`subtitle-${i}`"
+      :x="WIDTH / 2"
+      :y="subtitleStartY + i * subtitleLineHeight"
+      text-anchor="middle"
+      dominant-baseline="middle"
+      :font-size="subtitleFontSize"
+      fill="#64748b"
+    >
+      {{ line }}
+    </text>
+
     <!-- Empty state -->
     <text
       v-if="insufficientCriteria"

src/storage.ts

@@ -9,7 +9,9 @@ function loadAll(): Radar[] {
     const raw = localStorage.getItem(STORAGE_KEY)
     if (!raw) return []
     const parsed = JSON.parse(raw)
-    return Array.isArray(parsed) ? parsed : []
+    if (!Array.isArray(parsed)) return []
+    // Default concept for radars saved before the field existed.
+    return parsed.map((r: Radar) => ({ ...r, concept: r.concept ?? '' }))
   } catch {
     return []
   }
@@ -80,6 +82,7 @@ export function useRadars() {
     const radar: Radar = {
       id: uid(),
       name,
+      concept: '',
       criteria,
       profiles,
       scores: {},

src/types.ts

@@ -12,6 +12,8 @@ export type Profile = {
 export type Radar = {
   id: string
   name: string
+  /** Short subtitle naming the product and its typical performances. May be empty. */
+  concept: string
   criteria: Criterion[]
   profiles: Profile[]
   /** scores[profileId][criterionId] = 0..5 */

src/views/RadarEditor.vue

@@ -26,6 +26,12 @@ function setName(name: string): void {
   })
 }
 
+function setConcept(concept: string): void {
+  update(props.id, (r) => {
+    r.concept = concept
+  })
+}
+
 const chartContainer = ref<HTMLElement | null>(null)
 const toast = ref<{ kind: 'success' | 'error'; text: string } | null>(null)
 
@@ -70,19 +76,29 @@ async function copyPng(): Promise<void> {
 <template>
   <section v-if="radar" class="max-w-6xl mx-auto px-6 py-8">
     <!-- Top bar -->
-    <div class="flex flex-wrap items-center gap-3 mb-6">
-      <button class="btn btn-ghost btn-sm" @click="router.push({ name: 'list' })">
+    <div class="flex flex-wrap items-start gap-3 mb-6">
+      <button class="btn btn-ghost btn-sm mt-1" @click="router.push({ name: 'list' })">
         ← All radars
       </button>
+      <div class="flex-1 min-w-[200px] flex flex-col gap-2">
         <input
           type="text"
-        class="input input-bordered input-lg flex-1 min-w-[200px] font-semibold"
+          class="input input-bordered input-lg font-semibold"
           :value="radar.name"
           @input="setName(($event.target as HTMLInputElement).value)"
           placeholder="Untitled radar"
           aria-label="Radar name"
         />
-      <div class="flex gap-2">
+        <input
+          type="text"
+          class="input input-bordered input-sm"
+          :value="radar.concept"
+          @input="setConcept(($event.target as HTMLInputElement).value)"
+          placeholder="Concept — name the product and its typical performances"
+          aria-label="Radar concept"
+        />
+      </div>
+      <div class="flex gap-2 mt-1">
         <button class="btn btn-outline" @click="copyPng">Copy PNG</button>
         <button class="btn btn-primary" @click="downloadPng">Download PNG</button>
       </div>