fix(integrations): restrict Linear/Notion/Shopify hook deletion to admins (#15126)

Non-admin agents could delete an account's Linear, Notion, or Shopify
integration through the dedicated integration endpoints, which — unlike
the generic hooks endpoint — never checked the caller's role. This
restores the intended admin-only boundary for removing an integration.

## Closes
- https://linear.app/chatwoot/issue/CW-7383
- https://linear.app/chatwoot/issue/CW-7384
- https://linear.app/chatwoot/issue/CW-7189

## How to reproduce
As a non-admin **agent**, `DELETE
/api/v1/accounts/:id/integrations/{linear,notion,shopify}` returned
`200` and removed the account-wide integration. After this change it
returns `401` and the integration is preserved; administrators can still
remove it.

## What changed
- Route integration-hook deletion through `HookPolicy` (admin-only) via
a shared `Integrations::BaseController`, matching the generic hooks
controller.

Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>

app/controllers/api/v1/accounts/integrations/base_controller.rb

@@ -0,0 +1,9 @@
+class Api::V1::Accounts::Integrations::BaseController < Api::V1::Accounts::BaseController
+  private
+
+  # Managing an integration hook (create/update/destroy) is admin-only, enforced via HookPolicy.
+  # Subclasses opt in per action with `before_action :check_authorization, only: [...]`.
+  def check_authorization
+    authorize(:hook)
+  end
+end