probe: downloadable executables for machines without Docker

Each release attaches selfphoneng-probe-linux-x64 and -arm64 (Node's single executable
applications: esbuild bundle + postject into the official Node binary, checked against
nodejs.org's SHASUMS256.txt), the bundle as selfphoneng-probe.cjs (Node 22+) and SHA256SUMS.
Built in binary.Dockerfile with BuildKit's local output, so Gitea's runner can build it too.
deploy/probe/selfphoneng-probe.service runs it under systemd, sandboxed.

apps/probe/package.json

@@ -7,5 +7,9 @@
   "scripts": {
     "start": "node src/index.ts",
     "typecheck": "tsc --noEmit"
+  },
+  "devDependencies": {
+    "esbuild": "0.28.2",
+    "postject": "1.0.0-alpha.6"
   }
 }