Replace search icon with initial letter and apply topic sorting

[yesshreyes]

No description provided.

[RajashekarRaju]

Computing the first‐character inside the Composable

• Topic.name is never null or empty, so firstOrNull()?.uppercase() ?: "?" and the “?” fallback aren’t needed.
• Putting this logic in the UI layer forces the Composable to handle string parsing and placeholder logic.

Solution

 * Keep `data class Topic(val name: String)` unchanged.
 * Create a separate UI model, e.g.:

   ```kotlin
   data class TopicUi(
     val name: String,
     val initial: String,
     val isBookmarked: Boolean
   )
   ```
 * In the ViewModel, after sorting `List<Topic>`, map each `Topic` → `TopicUi` by computing `initial = domain.name.first().uppercase()`.
 * In the Composable, simply use `Text(text = topicUi.initial)`.

UI and domain models are mixed

• When UI logic (like extracting an initial) lives in the Composable, any change to how you compute or display that character requires touching multiple UI files.

Solution

By introducing TopicUi and mapping inside the ViewModel, all string‐manipulation stays in one place. The UI only displays already‐prepared fields.