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/models.py

@@ -90,6 +90,21 @@ class JoinStatusForm(FormModel):
         return value
 
 
+class InviteClaimForm(FormModel):
+    username: str = Field(min_length=3, max_length=32)
+    email: str = Field(min_length=3, max_length=255)
+    password: str = Field(min_length=6, max_length=128)
+    password_confirm: str = Field(min_length=6, max_length=128)
+    terms: bool = False
+
+    @field_validator("username")
+    @classmethod
+    def check_username(cls, value):
+        if not re.fullmatch(r"[A-Za-z0-9_-]{3,32}", value or ""):
+            raise ValueError("Use 3 to 32 letters, digits, _ or -")
+        return value
+
+
 class RoleForm(FormModel):
     role: str