i18n: refresh landing.hero subtitle + trustLine with AI/offline/AGPLv3 USPs

Phase 1 D1.8 — the home-page hero leads with three defensible
differentiators Velxio has that the dominant alternative doesn't:

  - AI agent integrated (Wokwi has none)
  - Works offline as a desktop app (Wokwi is cloud-only)
  - AGPLv3 open source (Wokwi is proprietary)

Subtitle and trustLine rewritten across all four shipped locales
(en, es, pt-br, zh-cn). No layout change — the LandingPage.tsx
component renders both strings already.

The competitor name isn't mentioned anywhere — the user comparing
side-by-side does the math themselves. Anchoring on the USPs makes
the eventual /pricing visit ("Maker $7 = AI included") land in
context instead of cold.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/i18n/locales/en/common.json

@@ -31,10 +31,10 @@
     "hero": {
       "titleLine1": "Arduino, ESP32 & Raspberry Pi.",
       "titleAccent": "Right in your browser.",
-      "subtitle": "Write code, wire up components, hit run. 19 boards, 48+ parts, real CPU emulation — no hardware, no installation, no cloud.",
+      "subtitle": "Write code, wire up components, hit run. 19 boards, an AI agent that builds circuits for you, real CPU emulation, full offline desktop app, AGPLv3 open source.",
       "ctaPrimary": "Try Simulator Free Online →",
       "ctaGithub": "View on GitHub",
-      "trustLine": "No signup required · Runs 100% in your browser · Free & open-source",
+      "trustLine": "AI agent included · Works offline · Open source AGPLv3 · No signup needed",
       "imageAlt": "Velxio editor with Arduino Uno traffic-light circuit"
     },
     "boards": {

frontend/src/i18n/locales/es/common.json

@@ -31,10 +31,10 @@
     "hero": {
       "titleLine1": "Arduino, ESP32 y Raspberry Pi.",
       "titleAccent": "Directamente en tu navegador.",
-      "subtitle": "Escribe código, conecta componentes, pulsa ejecutar. 19 placas, más de 48 componentes, emulación real de CPU — sin hardware, sin instalación, sin nube.",
+      "subtitle": "Escribí código, conectá componentes, ejecutá. 19 placas, un agente de IA que arma circuitos por vos, emulación real de CPU, app de escritorio offline, código abierto AGPLv3.",
       "ctaPrimary": "Probar el simulador online gratis →",
       "ctaGithub": "Ver en GitHub",
-      "trustLine": "No requiere registro · Funciona 100% en tu navegador · Gratuito y de código abierto",
+      "trustLine": "Agente de IA incluido · Funciona offline · Código abierto AGPLv3 · Sin registro",
       "imageAlt": "Editor de Velxio con circuito de semáforo en Arduino Uno"
     },
     "boards": {

frontend/src/i18n/locales/pt-br/common.json

@@ -31,10 +31,10 @@
     "hero": {
       "titleLine1": "Arduino, ESP32 e Raspberry Pi.",
       "titleAccent": "Direto no seu navegador.",
-      "subtitle": "Escreva código, monte componentes, aperte o play. 19 placas, mais de 48 componentes, emulação real de CPU — sem hardware, sem instalação, sem nuvem.",
+      "subtitle": "Escreva código, conecte componentes, execute. 19 placas, um agente de IA que monta circuitos para você, emulação real de CPU, app desktop offline, código aberto AGPLv3.",
       "ctaPrimary": "Experimente o Simulador Grátis Online →",
       "ctaGithub": "Ver no GitHub",
-      "trustLine": "Sem cadastro · Roda 100% no navegador · Gratuito e de código aberto",
+      "trustLine": "Agente de IA incluído · Funciona offline · Código aberto AGPLv3 · Sem cadastro",
       "imageAlt": "Editor Velxio com circuito de semáforo Arduino Uno"
     },
     "boards": {

frontend/src/i18n/locales/zh-cn/common.json

@@ -31,10 +31,10 @@
     "hero": {
       "titleLine1": "Arduino、ESP32 和 Raspberry Pi。",
       "titleAccent": "就在你的浏览器中。",
-      "subtitle": "编写代码，连接元件，点击运行。19 种开发板、48 多个部件、真实的 CPU 仿真——无需硬件，无需安装，无需云。",
+      "subtitle": "编写代码、连接元件、运行。支持 19 块开发板，AI 智能助手为你搭建电路，真实 CPU 仿真，完整离线桌面应用，AGPLv3 开源。",
       "ctaPrimary": "免费在线试用模拟器 →",
       "ctaGithub": "在 GitHub 上查看",
-      "trustLine": "无需注册 · 100% 在浏览器中运行 · 免费且开源",
+      "trustLine": "内置 AI 助手 · 离线可用 · AGPLv3 开源 · 无需注册",
       "imageAlt": "Velxio 编辑器中的 Arduino Uno 交通灯电路"
     },
     "boards": {