feat: Secure external credentials with database encryption (#12648)

## Changelog

- Added conditional Active Record encryption to every external
credential we store (SMTP/IMAP passwords, Twilio tokens,
Slack/OpenAI hook tokens, Facebook/Instagram tokens, LINE/Telegram keys,
Twitter secrets) so new writes are encrypted
whenever Chatwoot.encryption_configured? is true; legacy installs still
receive plaintext until their secrets are
    updated.
- Tuned encryption settings in config/application.rb to allow legacy
reads (support_unencrypted_data) and to extend
deterministic queries so lookups continue to match plaintext rows during
the rollout; added TODOs to retire the
    fallback once encryption becomes mandatory.
- Introduced an MFA-pipeline test suite
(spec/models/external_credentials_encryption_spec.rb) plus shared
examples to
verify each attribute encrypts at rest and that plaintext records
re-encrypt on update, with a dedicated Telegram case.
The existing MFA GitHub workflow now runs these tests using the
preconfigured encryption keys.

fixes:
https://linear.app/chatwoot/issue/CW-5453/encrypt-sensitive-credentials-stored-in-plain-text-in-database

## Testing Instructions

 1. Instance without encryption keys
- Unset ACTIVE_RECORD_ENCRYPTION_* vars (or run in an environment where
they’re absent).
      - Create at least one credentialed channel (e.g., Email SMTP).
- Confirm workflows still function (send/receive mail or a similar
sanity check).
- In the DB you should still see plaintext values—this confirms the
guard prevents encryption when keys are missing.
  2. Instance with encryption keys
      - Configure the three encryption env vars and restart.
- Pick a couple of representative integrations (e.g., Email SMTP +
Twilio SMS).
      - Legacy channel check:
- Use existing records created before enabling keys. Trigger their
workflow (send an email / SMS, or hit the
            webhook) to ensure they still authenticate.
- Inspect the raw column—value remains plaintext until changed.
      - Update legacy channel:
- Edit one legacy channel’s credential (e.g., change SMTP password).
- Verify the operation still works and the stored value is now encrypted
(raw column differs, accessor returns
            original).
      - New channel creation:
- Create a new channel of the same type; confirm functionality and that
the stored credential is encrypted from
            the start.

---------

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/models/integrations/hook.rb

@@ -21,6 +21,9 @@ class Integrations::Hook < ApplicationRecord
   before_validation :ensure_hook_type
   after_create :trigger_setup_if_crm
 
+  # TODO: Remove guard once encryption keys become mandatory (target 3-4 releases out).
+  encrypts :access_token, deterministic: true if Chatwoot.encryption_configured?
+
   validates :account_id, presence: true
   validates :app_id, presence: true
   validates :inbox_id, presence: true, if: -> { hook_type == 'inbox' }