Disable session resume UI for worktree chats

[mcintyre94]

Summary

• Session suggestions view is hidden when a chat has a worktree (worktrees are always fresh, nothing to resume)
• fetchRemoteSessions exits early when worktreePath is set, avoiding a wasteful exec call
• worktreePath changed from private to private(set) so ChatView can read it

Test plan

• Open a chat with worktrees enabled — confirm no session suggestions UI appears on the empty chat screen
• Open a chat without worktrees — confirm session suggestions still load and display normally

🤖 Generated with Claude Code

[claude]

Code review

Missing unit test for modified view model logic (CLAUDE.md)

CLAUDE.md requires: "Add new unit tests when adding or modifying logic (models, parsers, utilities, view models)"

fetchRemoteSessions in ChatViewModel.swift has a new conditional code path (early return when worktreePath != nil), but no test was added to WispTests/ChatViewModelTests.swift. There is also no pre-existing coverage for this function.

A test verifying that fetchRemoteSessions is a no-op when worktreePath is set would be expected — e.g. assert that remoteSessions stays empty and no exec call is made when a worktree path is present.

Relevant code:

wisp/Wisp/ViewModels/ChatViewModel.swift

Lines 226 to 231 in 1b9c8ca

	func fetchRemoteSessions(apiClient: SpritesAPIClient, existingSessionIds: Set<String>) {
	// Worktrees are always fresh — no sessions to resume
	guard worktreePath == nil else { return }
	guard !isLoadingRemoteSessions else { return }
	isLoadingRemoteSessions = true