fix: defer sidebar actions until resource loads

[fredrikblau]

Description

The Actions panel can stay mounted while the sidebar switches resources. During that gap it resolves actions with a null resource and can throw before the shares selection finishes loading.

Return no actions until the resource is available. A regression test covers the loading state.

Related Issue

• Fixes Actions sidebar panel may cause errors on shares page #3297

How Has This Been Tested?

• test environment: Node 24.20.0, pnpm 11.25.0
• test case 1: FileActions unit suite (3 passed)
• test case 2: full unit suite (3,916 passed, 6 skipped, 11 todo)
• test case 3: type checks, lint, formatting, and production build

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)