Document a pre-upload Marketplace smoke test

[redcatbear]

Situation

JetBrains recommends confirming that a plugin works correctly by installing the plugin from disk in a fresh target IDE before deployment. The project has manualTestIde and GitHub release installation instructions, but no explicit pre-upload smoke-test checklist for the signed Marketplace artifact.

Relevant docs: https://plugins.jetbrains.com/docs/intellij/publishing-plugin.html

Out-of-Scope

• Automating all manual UI checks.
• Adding new plugin features.
• Changing supported IDE versions.
• Performing the Marketplace upload.

Acceptance Criteria

1. A pre-upload smoke-test checklist exists in project documentation.
2. The checklist uses the signed ZIP artifact intended for Marketplace upload, not an unsigned development ZIP.
3. The checklist covers installation from disk in a fresh supported IDE instance.
4. The checklist verifies the main user workflows: live templates, completion, navigation, trace action, run configuration, and help action.
5. Release documentation states that Marketplace upload must wait until the smoke test has passed.