Publish cesiumjs-mcp to npm to eliminate local clone requirement

[MKartaviciute]

Context

Depends on #35 (cesiumjs-mcp gateway package). Once the gateway exists as a buildable package, publishing it to npm removes the last remaining friction blocker from #34 -- users no longer need to clone the repo or run a build.

Current state (after #35)

Users still need to:

1. Clone the repo
2. Run pnpm install && pnpm run build
3. Point their config at an absolute local path

Goal

Once published, the entire setup becomes:

{
  "cesium": {
    "type": "stdio",
    "command": "npx",
    "args": ["-y", "cesiumjs-mcp@latest"]
  }
}

No clone. No build. No absolute paths.

Proposed Implementation

1. Package configuration (servers/gateway/package.json)

• Set "name": "cesiumjs-mcp" and "version": "1.0.0"
• Add a "bin" entry pointing at the compiled entry point
• Add "files" array to include only the build/ output
• Set "publishConfig": { "access": "public" }

2. GitHub Actions publish workflow (.github/workflows/publish-cesiumjs-mcp.yml)

Trigger: push of a tag matching cesiumjs-mcp@*

Steps:

• Checkout
• Setup Node 22 + pnpm
• pnpm install
• pnpm run build (shared + gateway only)
• npm publish --workspace servers/gateway

3. Version strategy

Follow the existing monorepo pattern -- gateway version is independent of domain server versions. Each domain package can still be published or kept private separately.

Acceptance Criteria

• npx -y cesiumjs-mcp@latest starts the gateway without a local clone
• Package is listed on npmjs.com as cesiumjs-mcp
• GitHub Actions workflow publishes automatically on cesiumjs-mcp@x.y.z tag push
• README.md updated to show the npx one-liner as the primary setup path

Out of Scope

• Publishing individual domain packages (@cesium-mcp/camera-server, etc.)
• Semantic release or automated changelog (can be a follow-up)