Codebase audit: remove dead code, fix broken patterns, consolidate duplicates; v2.0.27

- Remove unused prop-types dep, deprecated useOutboundLinkTracking export
- Fix missing linkClicks key in analyticsEvents initial state (B-01)
- Export ADMIN_SESSION_COOKIE from auth.js; remove local copy in admin-auth.js (D-02)
- Remove cookieFlags() wrapper in auth.js and study-helpers.js; use cookieSecureFlag() directly (U-04)
- Remove ADMIN_SESSION_TTL_MS duplicate from config.js (D-01)
- Remove DEFAULT_SEO/DEFAULT_LEGAL/DEFAULT_REDIRECT_RULES/DEFAULT_PODCAST_FEATURED_LINKS/DEFAULT_PUBLISH_STATE
  duplicates from config.js; re-export from helpers.js (D-04, fixes sitemapPaths divergence)
- Fix email.js hardcoded fallback strings to use DEFAULT_RESEND_TO/DEFAULT_RESEND_REPLY_TO (M-02)
- Remove duplicate normalizeIp, isPrivateOrLocalIp, normalizeRedirectPath, sanitizeUrl,
  sanitizeRedirectRules bodies from study-helpers.js; re-export from helpers.js (D-03)
- Fix pruneStatsByDays to import VISITOR_RETENTION_DAYS_DEFAULT from config.js (B-02)
- Fix createTitusDownloadToken to use DOWNLOAD_TOKEN_TTL_MS constant (B-03)
- Remove normalizeMessageType duplicate from study-helpers.js (U-03/D-08)
- Remove dead wantsWelcome variable in contact.js; use shouldSendWelcome (B-04)
- Replace dynamic imports in contact.js with static imports (B-07)
- Remove dead wantsWelcome=true in study-auth.js (B-05)
- Merge duplicate import blocks in analytics.js and public.js (D-05, D-06)
- Replace dynamic readFile re-import in nuggets-host-upload.js (B-06)
- Replace hardcoded SITE_URL fallbacks with getCanonicalBaseUrl() (M-06)
- Replace raw resend.emails.send in study-account.js with sendResendEmailWithRetry (M-01)

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

server/routes/study-auth.js

@@ -105,7 +105,6 @@ export function register(app) {
     queueStudyUsersWrite()
 
     if (subscribe) {
-      const wantsWelcome = true
       const submission = {
         id: randomUUID(),
         submittedAt: now,
@@ -113,9 +112,9 @@ export function register(app) {
         email: username,
         message: '',
         messageType: 'general',
-        subscribe: wantsWelcome,
+        subscribe: true,
         archived: false,
-        emailStatus: normalizeContactEmailStatus(null, wantsWelcome),
+        emailStatus: normalizeContactEmailStatus(null, true),
       }
       state.contactSubmissions.unshift(submission)
       state.contactSubmissions = state.contactSubmissions.slice(0, MAX_CONTACT_SUBMISSIONS)