Retire the Node server in favor of Rust

[danshapiro]

Summary

• Make the Rust server the canonical backend across development, startup, tests, Electron, containers, and CI.
• Remove the legacy Node application server while retaining only sanctioned Node tooling and Claude sidecar support.
• Preserve the Rust-only feature triage and cutover receipts.

Verification

• RUST_TEST_THREADS=1 npm run test:rust on rebased branch — passed (3,636 passed, 0 failed, 8 ignored).
• npm run typecheck on rebased branch — passed.
• Source-runtime smoke, Rust server checks, Electron tests, lint, and formatting passed in the recorded receipts.
• Installed the required Ubuntu Rust/Tauri development packages, including libdbus-1-dev.
• No live port 3001 restart or health check was performed.

Notes

• The branch was rebased onto current origin/main and the PR conflict is resolved.
• The coordinated JavaScript gate retains the two base-reproduced EnvHttpProxyAgent stderr assertions documented in the receipts.