fix: restore token access to account APIs (#15088)

Token-authenticated requests to Agent Bots, Labels, and affected Captain
endpoints return normal responses again. The regression was caused by
duplicate `current_account` callbacks in subclasses moving account
resolution behind the API entitlement check, leaving `Current.account`
unset.

## Closes

- https://linear.app/chatwoot/issue/CW-7641/5xx-errors-in-agent-bot-apis

## How to reproduce

1. Send `GET /api/v1/accounts/:account_id/agent_bots` with a valid
administrator API access token.
2. Observe a `500` from `validate_token_api_access` because
`Current.account` is `nil`.
3. With this change, account resolution runs in the base-controller
order and the request succeeds.

## What changed

- Removed redundant `current_account` callbacks from account-scoped
controllers that already inherit the callback from
`Api::V1::Accounts::BaseController`.
- Kept the standalone direct-upload controller callback unchanged.
- Added regression coverage for administrator API-token access to Agent
Bots.

app/controllers/api/v1/accounts/agent_bots_controller.rb

@@ -1,5 +1,4 @@
 class Api::V1::Accounts::AgentBotsController < Api::V1::Accounts::BaseController
-  before_action :current_account
   before_action :check_authorization
   before_action :agent_bot, except: [:index, :create]
 

app/controllers/api/v1/accounts/captain/preferences_controller.rb

@@ -1,5 +1,4 @@
 class Api::V1::Accounts::Captain::PreferencesController < Api::V1::Accounts::BaseController
-  before_action :current_account
   before_action :authorize_account_update, only: [:update]
 
   def show

app/controllers/api/v1/accounts/labels_controller.rb

@@ -1,5 +1,4 @@
 class Api::V1::Accounts::LabelsController < Api::V1::Accounts::BaseController
-  before_action :current_account
   before_action :fetch_label, except: [:index, :create]
   before_action :check_authorization