feat(marketing): exempt public blueprints from noindex + fix / route collision

- add_no_crawl_headers now skips marketing.*, legal.*, billing.success,
  static, and robots_txt endpoints via _is_public_indexable_endpoint
  helper; all other routes keep the X-Robots-Tag noindex header
- recordings.index drops @login_required and instead redirects
  anonymous users to marketing.landing, resolving the URL-map
  collision between recordings_bp and marketing_bp at "/"
- robots.txt rewritten: public marketing pages and /legal/* allowed,
  /api/, /admin, /account, /share/, /app/, /checkout, /login, /signup,
  /webhooks/ disallowed; Googlebot, Bingbot, ClaudeBot, GPTBot,
  PerplexityBot, Applebot explicitly allowed
- New tests/test_no_crawl_headers.py (14 tests) covers exemption
  helper + integration on /, /robots.txt, /static, /admin, /login
- New tests/test_marketing_root_redirect.py (4 tests) verifies
  anonymous users at / never get a /login redirect

Tests verified via AST + logic walkthrough; pytest blocked on Windows
by pre-existing fcntl import in src/init_db.py (B-1.2 limitation).

src/app.py

@@ -654,12 +654,40 @@ from src.config.startup import initialize_file_monitor, get_file_monitor_functio
 run_startup_tasks(app)
 
 # --- No-Crawl System: HTTP Headers ---
+# Endpoints that must remain indexable by search engines and AI crawlers.
+# Public marketing/legal/billing-success pages are exempted from the
+# X-Robots-Tag noindex header so they can be discovered (Loi 25 transparency,
+# GEO/SEO strategy). All other routes (api, admin, account, share, app, auth,
+# recordings dashboard, etc.) keep the noindex header as defense-in-depth.
+_PUBLIC_INDEXABLE_PREFIXES = ('marketing.', 'legal.')
+_PUBLIC_INDEXABLE_ENDPOINTS = frozenset({
+    'billing.success',  # post-payment confirmation page (added in B-2.7)
+    'robots_txt',       # served from /robots.txt
+    'static',           # static asset serving
+})
+
+
+def _is_public_indexable_endpoint(endpoint):
+    """Return True if the resolved endpoint should NOT receive noindex headers."""
+    if not endpoint:
+        return False
+    if endpoint in _PUBLIC_INDEXABLE_ENDPOINTS:
+        return True
+    return endpoint.startswith(_PUBLIC_INDEXABLE_PREFIXES)
+
+
 @app.after_request
 def add_no_crawl_headers(response):
     """
     Add HTTP headers to discourage search engine crawling and indexing.
     This provides defense-in-depth alongside robots.txt and meta tags.
+
+    Marketing pages, legal pages, and the post-payment success page are
+    exempted so they remain indexable by search engines and AI crawlers.
     """
+    if _is_public_indexable_endpoint(request.endpoint):
+        return response
+
     response.headers['X-Robots-Tag'] = 'noindex, nofollow, noarchive, nosnippet, noimageindex'
     return response