feat: packages/email — Maizzle v6 + Tailwind CSS v4 HTML email templates

- New @sexy.pivoine.art/email package with @maizzle/framework@6.0.0-15
- Uses @maizzle/tailwindcss (TW v4 preset) with @theme brand tokens
  derived from the frontend's app.css oklch primary color
- LightningCSS automatically lowers oklch/lab to hex for email clients
- Real HTML template files (templates/layouts/main.html, verification.html,
  password-reset.html) — not JS template strings
- PostCSS `from` override so @import "@maizzle/tailwindcss" resolves from
  the email package's own node_modules
- Backend lib/email.ts now calls renderVerification/renderPasswordReset
  instead of inline HTML strings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile.backend

@@ -16,6 +16,7 @@ COPY packages/backend/package.json ./packages/backend/package.json
 COPY packages/frontend/package.json ./packages/frontend/package.json
 COPY packages/buttplug/package.json ./packages/buttplug/package.json
 COPY packages/types/package.json ./packages/types/package.json
+COPY packages/email/package.json ./packages/email/package.json
 
 RUN pnpm install --frozen-lockfile --filter @sexy.pivoine.art/backend --ignore-scripts
 
@@ -23,8 +24,11 @@ RUN pnpm install --frozen-lockfile --filter @sexy.pivoine.art/backend --ignore-s
 RUN pnpm rebuild argon2 sharp
 
 COPY packages/types ./packages/types
+COPY packages/email ./packages/email
 COPY packages/backend ./packages/backend
 
+RUN pnpm --filter @sexy.pivoine.art/email build
+
 RUN pnpm --filter @sexy.pivoine.art/backend build
 
 RUN CI=true pnpm install --frozen-lockfile --filter @sexy.pivoine.art/backend --prod --ignore-scripts