UI: show the serving binary version in the header

[rarepops]

What problem does this solve?

The browser management UI does not show which codebase-memory-mcp binary version is serving it. That makes support reports and upgrade verification harder, especially when a long-lived daemon or multiple install channels may leave uncertainty about the active binary. The frontend package version is not sufficient because it can differ from the release version of the server embedding it.

Proposed solution

• Add the serving binary's compiled CBM_VERSION to the existing GET /api/ui-config response.
• Show a compact read-only vX.Y.Z label beside the Codebase Memory name in the UI header.
• Hide the label when the config request fails or returns no valid version, preserving compatibility and avoiding a new error state.
• Cover the backend response with the native HTTP test and the visible label with a focused component test.

This reuses an existing same-origin endpoint and requires no new MCP method, external request, dependency, or configuration key.

Alternatives considered

• Use the version from graph-ui/package.json: this identifies the frontend package, not necessarily the binary serving it.
• Ask users to run codebase-memory-mcp --version: useful in a terminal, but it does not identify the server behind the currently open browser tab.
• Add a dedicated status endpoint: unnecessary for one small read-only field already suited to /api/ui-config.

Confirmations

• I searched existing issues and pull requests and this is not a duplicate.

[rarepops]

Related follow-up: #1821 tracks an explicit, user-triggered update check and source-aware copyable command. Actual one-click activation is intentionally deferred to a separate security and lifecycle design.