Isolate the Folder Option stuff to be replaced with the bigger worktree/folder/branch picker that copilot cli uses

[TylerLeonhardt]

Functionally no change, just refactoring.

[Copilot]

Pull request overview

This PR refactors Claude chat-session “folder option” group logic into a dedicated builder to better align with the larger worktree/folder/branch picker pattern used by the Copilot CLI, while keeping behavior the same.

Changes:

• Extract folder option-group building/mutation into a new ClaudeFolderOptionBuilder, and update ClaudeSessionOptionBuilder to orchestrate permission mode + delegated folder groups via a proxy input-state pattern.
• Move folder-related unit tests out of claudeSessionOptionBuilder.spec.ts into a new claudeFolderOptionBuilder.spec.ts.
• Extend fork-handler tests to assert session state (permission mode + folder info) is copied to the forked session.

Show a summary per file

File	Description
extensions/copilot/src/extension/chatSessions/vscode-node/test/claudeSessionOptionBuilder.spec.ts	Removes folder-related tests now covered by the new folder builder test suite.
extensions/copilot/src/extension/chatSessions/vscode-node/test/claudeFolderOptionBuilder.spec.ts	New test suite covering folder option group building, input-state rebuild/lock, and default folder resolution.
extensions/copilot/src/extension/chatSessions/vscode-node/test/claudeChatSessionContentProvider.spec.ts	Strengthens fork tests to verify session state is propagated to the forked session.
extensions/copilot/src/extension/chatSessions/vscode-node/claudeSessionOptionBuilder.ts	Refactors to delegate folder groups to ClaudeFolderOptionBuilder and manages permission mode group directly.
extensions/copilot/src/extension/chatSessions/vscode-node/claudeFolderOptionBuilder.ts	New extracted implementation for folder option group construction and state mutation helpers.
extensions/copilot/src/extension/chatSessions/vscode-node/claudeChatSessionContentProvider.ts	Updates imports to reference FOLDER_OPTION_ID from the new folder builder module.

Copilot's findings

• Files reviewed: 6/6 changed files
• Comments generated: 0