[P0] Fix project -> Data navigation so users can input data

[kgarg2468]

Problem

Clicking a project in Data does not reliably land users in an editable data form, so users cannot input data.

Likely Root Causes

• Data page error path redirects immediately back to /data, hiding load failure context.
• Project switch flow can be blocked by stale unsaved-state guard behavior.

Scope

• Ensure selecting a valid project always opens its data workspace.
• Keep users on the project route when load fails and show actionable retry.
• Validate and repair project-switch flow when unsaved state exists.

Acceptance Criteria

• From /data, selecting any valid project opens /data?project=<id> and shows form inputs.
• User can edit and save in both Quick Start and Advanced tabs.
• On load error, user sees clear in-place error and retry action (no silent bounce to list view).

Suggested Files

• app/(app)/data/page.tsx
• components/projects/ProjectListView.tsx
• components/projects/ProjectSwitchGuard.tsx
• lib/store/business-store.ts