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/gallery.py

@@ -99,7 +99,8 @@ def sync_gallery():
             seen_hashes.append(phash)
             thumb_directory = existing.get("thumb_directory") if existing else None
             thumb_name = existing.get("thumb_name") if existing else None
-            if not thumb_directory or not blob_path(thumb_directory, thumb_name).exists():
+            changed = not existing or existing.get("phash") != str(phash)
+            if changed or not thumb_directory or not blob_path(thumb_directory, thumb_name).exists():
                 thumb_directory, thumb_name = write_blob(
                     existing["uid"] if existing else generate_uid(), "webp", _thumbnail_bytes(image)
                 )
@@ -108,6 +109,10 @@ def sync_gallery():
     return synced
 
 
+def missing_sources():
+    return [filename for filename, _, _ in GALLERY if not (config.MEDIA_SOURCE_DIR / filename).exists()]
+
+
 def gallery_items(kind):
     items = []
     for row in media_by_kind(kind):