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

Makefile

@@ -19,7 +19,7 @@ STAGING_ADMIN_PASSWORD ?= staging-admin-pass-1
 PYTEST := $(PY) -m pytest
 
 .PHONY: install dev prod test test-headed test-unit test-api test-e2e test-fast test-failed \
-	test-first-failure test-slowest test-cache-clean check-ui preflight coverage coverage-headed \
+	test-first-failure test-slowest test-cache-clean check-ui check-gallery preflight coverage coverage-headed \
 	coverage-html locust locust-headless screenshots screenshots-staging screenshots-production \
 	staging-refresh prune prune-dry-run tree tree-loc zip delete-pyc clean
 
@@ -73,6 +73,9 @@ test-cache-clean:
 check-ui: $(STAMP)
 	$(PY) -m $(PKG).gates
 
+check-gallery: $(STAMP)
+	$(PY) tools/gallery/check.py $(GALLERY_DIR)
+
 preflight: $(STAMP)
 	$(PY) -c "import $(PKG).main; print('import ok')"
 	$(PY) -m pyflakes $(PKG) tests