feat(web): show the Inspector version in the lower-right corner (#1639)

Display the single-source version (root package.json) in the web UI's
lower-right corner, in grey — matching the CLI and TUI. The browser can't read
the filesystem, so the version flows backend → browser via GET /api/config:

- Add `version?: string` to InitialConfigPayload; the web backend
  (webServerConfigToInitialPayload) reads it once via the shared
  readInspectorVersion() and tags it onto the payload.
- Add a `useInspectorVersion` hook mirroring useSandboxUrl/useServerListWritable.
- Add a presentational `VersionBadge` element rendered fixed lower-right, grey,
  non-interactive; styling lives in a `versionBadge` Text theme variant (no
  inline styles, --inspector-* tokens).
- Wire it into App.tsx.

Verified live: /api/config serves `version: "2.0.0"` and the badge renders
`v2.0.0` fixed at the lower-right in grey. Tests: useInspectorVersion (full
branch coverage), VersionBadge (unit + Storybook), web-server-config payload.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw

core/mcp/remote/node/server.ts

@@ -91,6 +91,12 @@ export interface InitialConfigPayload {
    * shows catalog CRUD affordances.
    */
   writable?: boolean;
+  /**
+   * The Inspector version (from the root `package.json`), so the browser — which
+   * can't read the filesystem the way the CLI/TUI do — can display it. Absent on
+   * a legacy backend that predates the field; the UI just shows nothing then.
+   */
+  version?: string;
 }
 
 export interface RemoteServerOptions {