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/routers/admin/index.py

@@ -2,7 +2,7 @@
 from fastapi import APIRouter, Request
 
 from molodetz.constants import SOFT_DELETE_TABLES
-from molodetz.database import all_posts, count_deleted, count_open_join_requests, count_users
+from molodetz.database import all_posts, count_deleted, count_media, count_open_join_requests, count_users
 from molodetz.responses import respond
 from molodetz.routers.admin._shared import admin_seo
 from molodetz.schemas.admin import AdminIndexOut
@@ -19,6 +19,8 @@ async def admin_index(request: Request):
         "open_joins": count_open_join_requests(),
         "user_count": count_users(),
         "deleted_count": sum(count_deleted(name) for name in SOFT_DELETE_TABLES),
+        "flyer_count": count_media("flyer"),
+        "meme_count": count_media("meme"),
         "seo": admin_seo(request, "Admin"),
     }
     return respond(request, "admin/index.html", ctx, model=AdminIndexOut)