Audit and lower the minimum supported VS Code version

[Perdolique]

Summary

Determine the real minimum supported VS Code version and lower it if the current ^1.125.0 requirement is stricter than the runtime needs.

Motivation

The extension uses established symbol, reference, CodeLens, configuration, and event APIs. The current minimum may be driven by the development runtime rather than a required extension API, which can unnecessarily exclude otherwise compatible installations.

Scope

• Inventory every VS Code API and JavaScript runtime feature used by the packaged extension.
• Choose and document a deliberate support policy rather than an arbitrary historical minimum.
• Adjust the emitted JavaScript target and engines.vscode only after runtime validation.
• Test the packaged VSIX against the oldest supported VS Code release and the current release in CI.
• Keep development tooling on modern Node.js where useful; do not couple the development Node version to the extension-host minimum without evidence.

Acceptance criteria

• A documented compatibility table identifies the oldest tested and current tested VS Code versions.
• The oldest supported version passes the full Extension Host suite and loads the packaged output without syntax errors.
• CI prevents accidental use of APIs newer than the declared minimum.
• If the minimum cannot be lowered, the issue records the exact API or runtime constraint and closes without changing the manifest.