Heavily simplify the VS Code backend code

[jviotti]

Signed-off-by: Juan Cruz Viotti jv@jviotti.com

[augmentcode]

🤖 Augment PR Summary

Summary: This PR refactors the VS Code extension backend to reduce indirection by consolidating most logic into vscode/src/extension.ts.

Changes:

• Removes the dedicated CommandExecutor, DiagnosticManager, PanelManager, and fileUtils modules.
• Inlines CLI invocation, lint/metaschema parsing, and diagnostic creation helpers directly in the extension entrypoint.
• Simplifies webview panel lifecycle management by working directly with vscode.WebviewPanel.
• Keeps panel state construction centralized via a buildPanelState helper and continues caching the CLI version.
• Updates the VS Code debug launch config to point extension tests at ../test/vscode.

Technical Notes: Lint, format-check, and metaschema commands are still executed in parallel and diagnostics are derived from parsed CLI position ranges.

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[augmentcode]

Review completed. 1 suggestions posted.

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[cubic-dev-ai]

No issues found across 7 files

[jviotti]

By being a little clever, the entire thing goes down to like 500 lines of code, which is great