Fix setup host confirmation preserving selected host

[cursor]

Summary

Fixes a setup regression introduced in the recent filesystem/setup flow changes where clicking Next could persist an empty host even though the host dropdown displayed the currently configured host.

Bug and impact:

• Trigger: a user has a config directory with discovered hosts and an existing/default host in the store, then clicks Next without changing the dropdown.
• Impact: the app calls saveHost(""), clearing the persisted host and routing the user back into setup with a broken/empty host selection.

Root cause:

• The Select display was controlled by host, but the Next button persisted selectedHost, which initializes to an empty string and only changes on dropdown interaction.

Fix:

• Persist the effective host (selectedHost || host) and disable Next when no host is available.
• Added a regression test for clicking Next without changing the dropdown, plus coverage that an empty host cannot be persisted.

Test Plan

• bun install
• bun --filter native test:unit -- src/components/widget/steps/setup-step.test.tsx

Docs

• No docs update needed

  

[github-actions]

	Warnings
⚠️	PR is marked WIP / draft — do not merge until ready for review.
⚠️	Please assign this PR to someone (usually yourself).

📋 PR Overview

Lines changed	75 (+74 / -1)
Files	1 added, 1 modified, 0 deleted
Draft / WIP	yes
Has Test Plan	yes
New UI components	no
New Storybook stories	no
New Rust modules	no
New TS source files	no
New tests	yes (1)
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

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