fix: label Chatwoot Mobile sessions instead of 'Unknown Device' (#14753)

## Description

Sessions created by logins from the Chatwoot Mobile app currently render
as "Unknown Device" in the dashboard sessions UI. The mobile app's HTTP
layer sends:

- Android: `User-Agent: okhttp/4.9.2`
- iOS: `User-Agent: Chatwoot/<build> CFNetwork/<v> Darwin/<v>`

Neither pattern is classifiable by the `browser` gem, so
\`browser_name\`, \`platform_name\`, and \`device_name\` all end up
"Unknown".

This change adds a backend-only fallback in
\`UserSessionTrackingService\`. When \`Browser.new(ua)\` returns
"Unknown Browser" and the UA matches a known Chatwoot Mobile pattern,
the labels are overridden to \`Chatwoot Mobile\` + \`Android\` /
\`iPhone\`. The Vue sessions list (\`ActiveSessions.vue\`) then renders
"Chatwoot Mobile on Android" or "Chatwoot Mobile on iPhone" with the
smartphone icon.

This is the immediate floor. A follow-up will add structured
\`X-Chatwoot-*\` headers from the mobile app so we can render full
version + device model.

Fixes INF-75.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

- Added specs

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] Any dependent changes have been merged and published in downstream
modules

app/services/user_session_tracking_service.rb

@@ -1,4 +1,11 @@
 class UserSessionTrackingService
+  # CFNetwork UAs cannot distinguish iPhone from iPad; both get labelled iPhone here.
+  LEGACY_MOBILE_UAS = [
+    { match: %r{\Aokhttp/}, platform: 'Android', device: 'Android' },
+    { match: %r{\AChatwoot/.*CFNetwork.*Darwin}, platform: 'iPhone', device: 'iPhone' }
+  ].freeze
+  private_constant :LEGACY_MOBILE_UAS
+
   def initialize(user:, request:, client_id:)
     @user = user
     @request = request
@@ -26,7 +33,7 @@ class UserSessionTrackingService
   def session_attributes
     browser = Browser.new(@request.user_agent)
 
-    {
+    attrs = {
       ip_address: @request.remote_ip,
       user_agent: @request.user_agent,
       browser_name: browser.name,
@@ -35,5 +42,22 @@ class UserSessionTrackingService
       platform_name: browser.platform.name,
       platform_version: browser.platform.version
     }
+
+    patch_for_legacy_mobile(attrs)
+  end
+
+  def patch_for_legacy_mobile(attrs)
+    return attrs unless attrs[:browser_name] == 'Unknown Browser'
+
+    hit = LEGACY_MOBILE_UAS.find { |m| @request.user_agent.to_s.match?(m[:match]) }
+    return attrs unless hit
+
+    attrs.merge(
+      browser_name: 'Chatwoot Mobile',
+      browser_version: nil,
+      platform_name: hit[:platform],
+      platform_version: nil,
+      device_name: hit[:device]
+    )
   end
 end

spec/services/user_session_tracking_service_spec.rb

@@ -47,6 +47,75 @@ RSpec.describe UserSessionTrackingService do
       expect(existing.reload.ip_address).to eq('8.8.8.8')
       expect(existing.last_activity_at).to be_within(1.second).of(Time.current)
     end
+
+    context 'with a Chatwoot Mobile legacy User-Agent' do
+      let(:request) do
+        instance_double(
+          ActionDispatch::Request,
+          user_agent: ua,
+          remote_ip: '8.8.8.8'
+        )
+      end
+
+      context 'when the UA is okhttp (Android Chatwoot Mobile)' do
+        let(:ua) { 'okhttp/4.9.2' }
+
+        it 'labels the session as Chatwoot Mobile on Android', :aggregate_failures do
+          service.create_or_update!
+
+          session = user.user_sessions.last
+          expect(session.browser_name).to eq('Chatwoot Mobile')
+          expect(session.browser_version).to be_nil
+          expect(session.platform_name).to eq('Android')
+          expect(session.platform_version).to be_nil
+          expect(session.device_name).to eq('Android')
+          expect(session.user_agent).to eq(ua)
+        end
+      end
+
+      context 'when the UA is CFNetwork (iOS Chatwoot Mobile)' do
+        let(:ua) { 'Chatwoot/3759 CFNetwork/3886.100.1 Darwin/27.0.0' }
+
+        it 'labels the session as Chatwoot Mobile on iPhone', :aggregate_failures do
+          service.create_or_update!
+
+          session = user.user_sessions.last
+          expect(session.browser_name).to eq('Chatwoot Mobile')
+          expect(session.browser_version).to be_nil
+          expect(session.platform_name).to eq('iPhone')
+          expect(session.platform_version).to be_nil
+          expect(session.device_name).to eq('iPhone')
+          expect(session.user_agent).to eq(ua)
+        end
+      end
+
+      context 'when the UA is a real browser (Firefox on Linux)' do
+        let(:ua) { 'Mozilla/5.0 (X11; Linux x86_64; rv:124.0) Gecko/20100101 Firefox/124.0' }
+
+        it 'does not override the Browser-derived metadata', :aggregate_failures do
+          service.create_or_update!
+
+          session = user.user_sessions.last
+          expect(session.browser_name).to eq('Firefox')
+          expect(session.platform_name).to eq('Generic Linux')
+          expect(session.device_name).not_to eq('Android')
+          expect(session.device_name).not_to eq('iPhone')
+        end
+      end
+
+      context 'when the UA is unknown but does not match any mobile pattern' do
+        let(:ua) { 'curl/8.4.0' }
+
+        it 'leaves the Unknown labels untouched', :aggregate_failures do
+          service.create_or_update!
+
+          session = user.user_sessions.last
+          expect(session.browser_name).to eq('Unknown Browser')
+          expect(session.platform_name).to eq('Unknown')
+          expect(session.device_name).to eq('Unknown')
+        end
+      end
+    end
   end
 
   describe '#update_activity!' do