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>

api/openapi.yaml

@@ -269,7 +269,7 @@ components:
             required: [name, type]
             properties:
               name: {type: string}
-              type: {type: string, enum: [jira, azure_devops, youtrack, demo]}
+              type: {type: string, enum: [jira, azure_devops, youtrack, wekan, demo]}
               baseUrl: {type: string}
               projectKey: {type: string}
               pollIntervalSec: {type: integer, minimum: 10}
@@ -277,7 +277,7 @@ components:
               consultantIds: {type: array, items: {type: string}}
               credentials:
                 type: object
-                description: "jira: {email, apiToken} · azure_devops: {organization, project, pat} · youtrack: {permanentToken} · demo: {}"
+                description: "jira: {email, apiToken} · azure_devops: {organization, project, pat} · youtrack: {permanentToken} · wekan: {username, password} (projectKey = board id) · demo: {}"
   schemas:
     Error:
       type: object