Add model selection feature with UI controls

- Add model selector dropdown in chat interface (Opus, Sonnet, Default)
- Model preference persists across sessions using workspace state
- Add model validation to prevent invalid selections
- Display confirmation messages when switching models
- Update Claude command to include --model flag when specific model selected
- Reorganize input controls layout for better UX
- Update documentation in README.md and CHANGELOG.md

CHANGELOG.md

@@ -4,6 +4,20 @@ All notable changes to the "claude-code-chat" extension will be documented in th
 
 Check [Keep a Changelog](http://keepachangelog.com/) for recommendations on how to structure this file.
 
+## [0.0.9] - 2025-06-19
+
+### Added
+- Model selector dropdown in the chat interface
+  - Located to the left of the tools selector at the bottom of the chat box
+  - Supports three models: Opus (most capable), Sonnet (balanced), and Default (smart allocation)
+  - Model preference is saved and persists across sessions
+  - Validates model selection to prevent invalid model names
+  - Shows confirmation message when switching models
+
+### Changed
+- Reorganized input controls into left-controls and right-controls sections for better layout
+- Claude command now includes the --model flag when a specific model is selected
+
 ## [0.0.8] - 2025-06-19
 
 ### Added