feat(ui): add workspace init confirmation before syncing

[tusharmath]

Summary

Add an explicit user consent prompt before syncing a workspace directory, preventing unintended data sharing with ForgeCode Services.

Context

Previously, invoking a sync on an uninitialized directory would immediately begin syncing and sharing its contents with ForgeCode Services without any user acknowledgment. This is a privacy-sensitive operation and users should be given a clear opportunity to accept or decline before the sync proceeds.

Changes

• Added a confirmation prompt in on_workspace_init that informs users their directory contents will be synced and shared with ForgeCode Services, with yes as the default answer.
• If the user declines, workspace initialization is aborted and a cancellation notice is printed to the console.
• Added a post-init guard in the sync flow: after calling on_workspace_init, the workspace is re-checked and if it still does not exist (because the user declined), the sync is aborted early rather than proceeding with stale state.

Key Implementation Details

The confirmation uses ForgeWidget::confirm with with_default(true), so pressing Enter accepts by default. The unwrap_or(false) on the result ensures any prompt failure safely cancels the operation. The guard added at the call-site after on_workspace_init keeps the sync path honest — it does not assume initialization succeeded.

Testing

# Run the main crate tests
cargo insta test --accept -p forge_main

# Manual verification — run forge on a new directory and decline the prompt
cargo run -- sync /tmp/test-new-dir
# Expected: prompt appears, typing 'n' prints cancellation notice and exits cleanly

# Accept the prompt
cargo run -- sync /tmp/test-new-dir
# Expected: workspace is initialized and sync proceeds normally