Fix Quick Query without an open workspace

[hugosmoreira]

What

• Store Quick Query files in workspace storage when available and fall back to extension-global storage when no workspace is open.
• Add regression coverage for both the fallback and the existing workspace-scoped behavior.
• Document the user-facing fix in the changelog.

Why

When VS Code has no open workspace, ExtensionContext.storageUri is undefined. Quick Query currently throws Workspace storage path is undefined before it can show its existing no-workspace guidance.

Impact

Quick Query now reaches the intended warning flow in an empty VS Code window while continuing to isolate files per workspace whenever workspace storage exists.

Fixes #1415

Validation

• Negative control: the new no-workspace regression failed with the reported Workspace storage path is undefined error before the fallback was applied.
• Focused unit tests: 2 passed.
• Full unit suite: 633 passed; the only two failures were unrelated Windows environment limitations (symlink creation denied and an unavailable 8.3 short-path fixture).
• TypeScript check passed.
• ESLint passed with zero warnings on changed TypeScript files.
• Prettier and Markdown lint passed.
• Full extension build and VSIX packaging passed.
• git diff --check passed.