Headless language server (Langium grammar + validators)

[eduardozf]

Context

ADR 0006 keeps the public AST/diagnostics decoupled precisely so the parser can move to Langium and power a headless language server. This is the foundation for editor tooling.

Scope

• Author the Langium grammar mirroring the current language.
• Reuse existing validators/diagnostics behind the LSP.
• Create packages/language-server (@wire-lang/language-server).
• Conformance tests against existing parser snapshots so the public API is unchanged.

Acceptance

• LSP provides diagnostics matching the CLI for the example circuits.
• Update ADR 0006 status and docs/MVP.md roadmap.