feat(site): loop a faithful copy of the app's recording capsule in the hero

Replace the press-to-play demo and the "see how it works" button with an
example that keeps playing on the right: hold Right Alt, the capsule appears
with live wave bars, elapsed time and the partial transcript, releasing shows
the processing bar, and the cleaned sentence is pasted at the cursor of a
notes window. It cycles through two samples per language.

- Same numbers as apps/desktop recording-tip: 9 bars with cos weights, 100 ms
  updates, 0.5 smoothing, +/-35% jitter, 2-28 px, per-bar colours, 120 px
  progress bar min(95, (1 - 1/(1 + 1.5t)) * 100)%.
- WCAG 2.2.2: a pause button; stops when off screen or the tab is hidden.
  Reduced motion shows one still frame. The animation is aria-hidden with a
  text description for screen readers. Chinese and Japanese transcripts
  appear three characters at a time.
- Add 404.html so unknown paths stop falling back to the landing page, delete
  the duplicate accept-invite.html (/accept-invite/ is canonical) and link it
  straight to /#download, and move the legal pages off the retired orange
  accent (primary button contrast 5.2:1).

site/src/i18n/index.ts

@@ -19,6 +19,11 @@ export interface TitledText {
   body: string
 }
 
+export interface DemoSample {
+  raw: string
+  clean: string
+}
+
 export interface FaqItem {
   q: string
   a: string
@@ -62,24 +67,28 @@ export interface Translations {
     subtitle: string
     hotkeyKey: string
     hotkeyAction: string
-    secondaryCta: string
     trust: string
     /** 방문자가 Windows가 아닐 때 다운로드 버튼 아래에 보인다. */
     windowsOnly: string
   }
   demo: {
-    title: string
+    /** figure 의 접근 가능한 이름 */
+    label: string
+    /** 화면 낭독용 설명. 애니메이션 자체는 aria-hidden 이다. */
+    description: string
     note: string
-    idle: string
-    listening: string
-    polishing: string
-    done: string
+    windowTitle: string
+    docLine: string
+    /** 캡슐의 처리 중 문구 */
+    processing: string
+    stateIdle: string
+    stateListening: string
+    statePolishing: string
+    stateDone: string
+    pause: string
     play: string
-    replay: string
-    rawLabel: string
-    cleanLabel: string
-    sampleRaw: string
-    sampleClean: string
+    /** raw 는 띄어쓰기 단위로 한 낱말씩 나타난다. */
+    samples: [DemoSample, DemoSample]
   }
   features: {
     title: string