Clean up npm test plumbing across workspaces

[MatiasFernandez]

Goal

Bring the monorepo's npm test plumbing closer to a conventional npm-workspaces setup: make the three workspaces (client, server, mcp-server) run tests consistently, remove a latent divergence between how the root and the workspaces invoked their tests, and drop a Node flag that is now a no-op. Behavioral no-op on the supported toolchain (Node pinned to 24.15.0 via .nvmrc) — verified npm test passes across all three workspaces.

What changed

server/package.json — the workspace had no scripts block at all, which is why the root had to cd server && npx vitest run as a workaround. Added a standard "test": "vitest run", so it can be driven like any other workspace.

package.json — the root test hand-chained three legs that each invoked their workspace differently (cd server && npx vitest run, npm test --workspace client, cd mcp-server && npx vitest run). Now:

• test → npm run test --workspaces --if-present (the documented mechanism for running a script across all workspaces).
• test:server / test:mcp → npm test --workspace <name>, consistent with the existing test:client, so all per-workspace legs route through the workspace's own script.

mcp-server/package.json + package.json — the mcp-server test script carried NODE_OPTIONS=--experimental-require-module to let CommonJS require() the ESM-only @modelcontextprotocol/sdk. On Node 24 that flag is a no-op: require(ESM) has been enabled by default since Node v23.0.0 / v22.12.0 / v20.19.0. The inline NODE_OPTIONS=... syntax is also POSIX-shell-only (breaks on Windows cmd.exe). So:

• Dropped the flag; the script is now just "vitest run" (matching server).
• Added "engines": { "node": ">=22.12" } to the root to make explicit the Node floor the flag used to paper over.

Removing the flag also eliminates the divergence class at its root: with no special flag, the root and workspace invocations can no longer differ.

Verification

• npm test passes across all three workspaces.
• npm run test:mcp → 95/95 pass, exit 0, no ExperimentalWarning, no ERR_REQUIRE_ESM, with the flag removed on Node 24.15.0.