Report the app version on /healthz

Build 116.

/healthz has always carried a 'build' field, but it is a hash of the listener
page's assets — a cache-busting token, not a version. So the only way to tell
what a campus Mac was actually running was to install something and watch the
hash move, which is how the last three updates were confirmed. With an updater
in the field, what version a machine is on is the first question anyone asks.

It now answers plainly: version and buildNumber, passed to the server child from
the running bundle. Checking a campus is a single unauthenticated request.

It found something immediately: this development Mac reported appBuild 112 while
the source tree was at 115, because deploying loose files over an installed
bundle leaves its package.json behind. A packaged install reports correctly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/main.js

@@ -440,6 +440,11 @@ function startServer() {
     execPath: nodeBin,
     env: Object.assign({}, process.env, {
       CT_FFMPEG: ffmpegPathForChildren(),
+      /* So /healthz can report the APP’s version rather than only an asset
+         hash. A campus Mac’s build was otherwise unknowable from the network,
+         which made confirming an update a matter of inference. */
+      CT_APP_VERSION: appBuild().version,
+      CT_APP_BUILD: appBuild().build,
       PORT: String(port),
       DATA_DIR: dataDir(),
       /* Where the spoken clips land, so the server can hand them to phones. */