feat(beta): add beta testing features and privacy policy page

Implemented comprehensive beta testing system with tier badges and
reorganized environment configuration for better maintainability.

Beta Testing Features:
- Beta banner component with dismissible state (localStorage)
- Auto-assign SUPPORTER tier to new registrations (env controlled)
- TierBadge component with SUPPORTER/COMFORT tier display
- Badge shown in Navbar, ProfilePage, and PublicProfilePage
- Environment variables: VITE_BETA_MODE, BETA_AUTO_SUPPORTER

Environment Configuration Reorganization:
- Moved .env files from root to frontend/ and backend/ directories
- Created .env.{development,production}{,.example} structure
- Updated docker-compose.yml to use env_file for frontend
- All env vars properly namespaced and documented

Privacy Policy Implementation:
- New /privacy route with dedicated PrivacyPage component
- Comprehensive GDPR/RODO compliant privacy policy (privacy.html)
- Updated CookieConsent banner to link to /privacy
- Added Privacy Policy links to all footers (HomePage, PublicFooter)
- Removed privacy section from About Us page

HTML Content System:
- Replaced react-markdown dependency with simple HTML loader
- New HtmlContentPage component for rendering .html files
- Converted about-us.md and how-it-works.md to .html format
- Inline CSS support for full styling control
- Easier content editing without React knowledge

Backend Changes:
- Registration auto-assigns SUPPORTER tier when BETA_AUTO_SUPPORTER=true
- Added accountTier to auth middleware and user routes
- Updated public profile endpoint to include accountTier

Files:
- Added: frontend/.env.{development,production}{,.example}
- Added: backend/.env variables for BETA_AUTO_SUPPORTER
- Added: components/BetaBanner.jsx, TierBadge.jsx, HtmlContentPage.jsx
- Added: pages/PrivacyPage.jsx
- Added: public/content/{about-us,how-it-works,privacy}.html
- Modified: docker-compose.yml (env_file configuration)
- Modified: App.jsx (privacy route, beta banner)
- Modified: auth.js (auto SUPPORTER tier logic)

backend/src/controllers/auth.js

@@ -81,6 +81,10 @@ async function register(req, res, next) {
       ? `${firstName} ${lastName}`
       : username;
 
+    // Check if beta auto-supporter is enabled
+    const betaAutoSupporter = process.env.BETA_AUTO_SUPPORTER === 'true';
+    const accountTier = betaAutoSupporter ? 'SUPPORTER' : 'BASIC';
+
     // Create user
     const user = await prisma.user.create({
       data: {
@@ -94,6 +98,7 @@ async function register(req, res, next) {
         verificationCode,
         verificationTokenExpiry,
         emailVerified: false,
+        accountTier,
         avatar: `https://ui-avatars.com/api/?name=${encodeURIComponent(displayName)}&background=6366f1&color=fff`,
       },
       select: {
@@ -104,6 +109,7 @@ async function register(req, res, next) {
         lastName: true,
         wsdcId: true,
         emailVerified: true,
+        accountTier: true,
         avatar: true,
         createdAt: true,
       },