feat(numbers): add number sequences store; restrict companysetting keys

- Add `numbers` store module with `list` and `update` methods backed by
  the `numbers` table (prefix, padding, next) per company.
- Add sql queries LIST_BY_COMPANY, GET_BY_COMPANY_AND_ID, UPDATE_...
- Regenerate and wire API docs for `numbers`.

companysetting:
- Remove the `delete` endpoint (settings are now upsert/read only).
- Restrict `set` to a fixed allow-list of keys:
  ui.theme, keys.tavily, keys.openrouter, labelprinter.addr, labelprinter.type.
- Drop DELETE_BY_COMPANY_AND_KEY sql and the delete store file.

Docs: update README, API.md, API.companysetting.md, API.numbers.md.

src/sql/companysetting.js

@@ -39,9 +39,3 @@ WHEN NOT MATCHED THEN
     INSERT (company_id, [key], value, frontend)
     VALUES (@companyId, @key, @value, @frontend);
 `;
-
-export const DELETE_BY_COMPANY_AND_KEY = `
-DELETE FROM companysetting
-WHERE company_id = @companyId
-  AND [key] = @key
-`;