fix(auto): align TabTemplate with required Car API level 6 and tintable icons

- TabTemplate is @RequiresCarApi(6); bump manifest minCarApiLevel from 2
  to 6 so the host doesn't reject the template at runtime.
- Use a proper anonymous TabCallback (androidx's TabCallback is not a
  Kotlin fun interface) and import top-level TabContents (it is not a
  nested type of TabTemplate); the lambda/nested references don't
  compile.
- Mark tab CarIcons tintable (CarColor.DEFAULT) so day-mode AAOS themes
  don't render white-on-white.
- Extract buildChannelRow to keep buildChannelsTemplate under the
  NestedBlockDepth detekt threshold.
- Clarify MAX_LIST_ITEMS KDoc (per-ListTemplate host constraint, not an
  API-level property).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

feature/auto/src/main/AndroidManifest.xml

@@ -33,10 +33,11 @@
             </intent-filter>
         </service>
 
-        <!-- TabTemplate requires Car API level 2 (androidx.car.app 1.2.0+) -->
+        <!-- TabTemplate is annotated @RequiresCarApi(6); the host throws HostException
+             if we claim a lower minCarApiLevel than any template we actually use. -->
         <meta-data
             android:name="androidx.car.app.minCarApiLevel"
-            android:value="2" />
+            android:value="6" />
     </application>
 
 </manifest>