Member invites, gallery resync, content and operator docs

- Invite flow: admin issue/revoke on join requests, public single-use
  claim links (hash-only tokens, 7-day expiry, no state reveal), claim
  creates the Member account and marks the request accepted
- Gallery: admin status page plus resync endpoint; sync refreshes
  thumbnails whose content changed; tools/gallery contract and checker
- Docs: public content page, admin-only operator runbook, api.md
  invite/gallery sections, all routes in the live API docs, docs
  reachability gate test
- Screenshots cover the new pages; version 1.0.18

molodetz/constants.py

@@ -57,7 +57,7 @@ NOTIFICATION_TYPES = {
     "system.maintenance": "Maintenance mode changed",
 }
 
-CRAWLER_PRIVATE_PREFIXES = ("/notifications", "/admin", "/profile")
+CRAWLER_PRIVATE_PREFIXES = ("/notifications", "/admin", "/profile", "/invite")
 
 CRAWLER_MARKERS = (
     "bot",
@@ -94,6 +94,7 @@ SETTINGS_DEFAULTS = {
     "rate_limit_window_seconds": "60",
     "session_max_age_days": "7",
     "session_remember_days": "30",
+    "invite_expiry_days": "7",
     "terms_version": "1",
     "friendly_404": "1",
     "audit_retention_days": "365",