- Replace customer_lookup "Search/display field" single dropdown with a
  free-text "Match field name(s)" input supporting multiple fields (semicolon-separated),
  matching the api_lookup UX pattern
- When customer_lookup type is selected in the job type editor, any existing
  api_lookup attributes are automatically removed (customer_lookup supersedes api_lookup)
- In the job create/edit form, api_lookup attributes are suppressed when the
  job type includes a customer_lookup (customer_lookup takes the place of api_lookup)
- Backend /customers/lookup endpoint already handled multi-field match_field;
  no PHP changes required for that path

- add API Lookup attribute type with alias, URL, format, match fields, and auto-fill config
- update job type create/edit forms to configure API lookup attributes
- add authenticated /api/proxy route for external lookup requests
- enhance job create/edit flow to load and select API lookup values
- rebuild jobs table columns dynamically from job type attributes
- add unsaved-changes guard for ct-form forms
- include related UI/style updates across job and job-type views