Docs catch-up + in-app Help page

README: the Catalog page description and a new "Fixing what the model
gets wrong" section cover the curation actions (edit/split/remove) and
their durability contract. Spec: amended-as-built notes — duplicate
same-edition copies are now supported via explicit splits, review is
both a TUI and the web app, and the data model lists the three curation
stores plus the dismissed-tickets file.

New Help page in the app (nav entry on every page): the six-stage flow,
what each page is for, the curation semantics with undo instructions, a
status-chip legend rendered with the real chips, keyboard shortcuts,
and where the data lives on disk.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jXZFSTZQKzAC8fqpWSz9g

tests/test_webreview.py

@@ -766,3 +766,12 @@ def test_remove_title_is_durable_and_drops_vetoed_rows(tmp_path):
         ).status_code
         == 404
     )
+
+
+def test_help_page_serves_and_is_in_nav(tmp_path):
+    web, _ = make_client(tmp_path)
+    res = web.get("/help")
+    assert res.status_code == 200
+    assert "Fixing the catalog" in res.text
+    # every page's nav includes the Help entry
+    assert 'href="/help"' in web.get("/").text