feat: WeKan ticketing source

- wekan connector: board id as project key, cards assigned to the
  consultant's WeKan username (assignees with member fallback), archived
  cards skipped, client-side modifiedAt since-filtering, username/password
  login with token reuse (or pre-issued token), case-insensitive identity
- fake-WeKan unit tests: factory validation, test-connection, fetch
  filtering, key listing, token reuse
- admin customer wizard: WeKan option + credential fields
- OpenAPI enum + credential shapes, README identity mapping docs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/static/js/admin.js

@@ -25,6 +25,8 @@ function credsFromForm(type) {
       return { organization: val('c-ado-org'), project: val('c-ado-project'), pat: val('c-ado-pat') };
     case 'youtrack':
       return { permanentToken: val('c-yt-token') };
+    case 'wekan':
+      return { username: val('c-wekan-user'), password: val('c-wekan-pass') };
     default:
       return {};
   }