chore: Add security flags to session cookie configuration (#14248)

## Summary
- Adds `httponly` and `secure` flags to session cookie configuration
- Adds RSpec tests for session configuration

## Changes
- `config/initializers/session_store.rb`: add `httponly: true`, `secure:
FORCE_SSL`
- `spec/config/session_store_spec.rb`: tests for all session store
options

Ref #2683 (hardens the session cookie but does not remove it, sessions
are still needed for super_admin dashboard)

---------

Co-authored-by: Adam-Relay <adam@userelay.ai>
Co-authored-by: Adam Berger <adam@adam-berger.com>
Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>

config/initializers/session_store.rb

@@ -1,3 +1,10 @@
 # Be sure to restart your server when you modify this file.
+# Sessions are used only for the super_admin dashboard (flash/CSRF), not for API auth.
 
-Rails.application.config.session_store :cookie_store, key: '_chatwoot_session', same_site: :lax
+secure_cookies = ActiveModel::Type::Boolean.new.cast(ENV.fetch('FORCE_SSL', false))
+
+Rails.application.config.session_store :cookie_store,
+                                       key: '_chatwoot_session',
+                                       same_site: :lax,
+                                       secure: secure_cookies,
+                                       httponly: true