feat: contact form via SMTP + 3D click links

Replace Frappe/Dolibarr API with direct SMTP send via
nodemailer. Form posts to local /api/submit-lead, no
external proxy on api.lelectronrare.fr (which was down
since Frappe was retired ~13 days ago).

Add onClick handler on BMU/I2C/MOSFET 3D meshes that
redirects to /contact/. Cursor pointer on hover for
affordance.

Switch Dockerfile from npm ci to npm install --no-audit
since package-lock will regen with nodemailer added.

Container env vars to configure:
  SMTP_HOST, SMTP_PORT, SMTP_USER, SMTP_PASS
  MAIL_FROM (defaults to SMTP_USER)
  MAIL_TO (defaults to contact@lelectronrare.fr)

package.json

@@ -33,6 +33,7 @@
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "motion": "^12.23.24",
+    "nodemailer": "^6.9.16",
     "postprocessing": "^6.39.0",
     "react": "^19.1.1",
     "react-dom": "^19.1.1",
@@ -41,6 +42,7 @@
   },
   "devDependencies": {
     "@astrojs/check": "^0.9.6",
+    "@types/nodemailer": "^6.4.16",
     "@storybook/addon-a11y": "^9.1.5",
     "@storybook/addon-docs": "^9.1.5",
     "@storybook/addon-onboarding": "^9.1.5",