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/schemas/admin.py

@@ -10,6 +10,14 @@ class AdminIndexOut(OutModel):
     open_joins: int = 0
     user_count: int = 0
     deleted_count: int = 0
+    flyer_count: int = 0
+    meme_count: int = 0
+
+
+class GalleryStatusOut(OutModel):
+    flyers: int = 0
+    memes: int = 0
+    missing: list[str] = []
 
 
 class AdminPostsOut(OutModel):