Add reusable channel array list controls and parsing utilities for channel forms.
Normalize channel string-array payloads in the backend, including pasted values,
numeric IDs, hidden characters, duplicates, and empty clears.
Also allow FlexibleStringSlice to unmarshal null values and cover the new behavior
with backend and config tests.
* refactor(web): load channel configs without exposing secret values
- add a dedicated channel config API that returns sanitized config plus
configured secret metadata
- update channel config pages and forms to use secret presence for
placeholders, validation, reset, and save behavior
- refresh the channel settings layout and clean up related i18n copy
- add backend tests for the new channel config endpoint
* fix(config): restore missing strings import
- persist Weixin bindings, enable the channel automatically, and try to restart the gateway
- refresh frontend channel and gateway state after successful binding
- harden QR polling state handling and update related channel UI behavior
- localize sidebar channel priority, add Weixin icon support, and add backend test coverage
