Run the tests on Node 22.16, and fix what a fresh setup tripped over

Node 22.16 runs TypeScript only behind --experimental-strip-types (on by
default from 22.18), so `npm test` failed on every file with
ERR_UNKNOWN_FILE_EXTENSION. The flag is harmless on newer versions.

probe and session-diagnose still imported dist/schulcloud/client.js, which
the move to core/ renamed, so both scripts died at import.

A relative MIRROR_DIR broke file serving: res.sendFile refuses a relative
path, and resolveWithin returns an absolute path only when its root is one.
The config resolves it once, at load.

package-lock.json is what `npm install` records today: the `schulcloud`
bin, and no stale peer flags. 101 tests.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -18,6 +18,7 @@
         "zod": "^3.25.76"
       },
       "bin": {
+        "schulcloud": "dist/bin/cli.js",
         "schulcloud-mcp": "dist/bin/stdio.js"
       },
       "devDependencies": {
@@ -981,7 +982,6 @@
       "resolved": "https://registry.npmjs.org/express/-/express-5.2.1.tgz",
       "integrity": "sha512-hIS4idWWai69NezIdRt2xFVofaF4j+6INOpJlVOLDO8zXGpUVEVzIYk12UUi2JzjEzWL3IOAxcTubgz9Po0yXw==",
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "accepts": "^2.0.0",
         "body-parser": "^2.2.1",
@@ -1269,7 +1269,6 @@
       "resolved": "https://registry.npmjs.org/hono/-/hono-4.13.7.tgz",
       "integrity": "sha512-c8/gF9ac8Y78/agExVocyLevgR+JlpNB444Py0FSX8pJoPdYUfUzRcXtYEYGwt6l19qIlVZPN5Mfsw9jFShmQQ==",
       "license": "MIT",
-      "peer": true,
       "engines": {
         "node": ">=16.9.0"
       }
@@ -1873,7 +1872,6 @@
       "resolved": "https://registry.npmjs.org/pg/-/pg-8.23.0.tgz",
       "integrity": "sha512-Ip2EQCngowJLGOfCwkFhPXU7/ljlhn6Rxlmy4XYfL2Y+vyRM59+8uR2xqRWKdYmbXmxCFOAmKxBuSUCdF34qLg==",
       "license": "MIT",
-      "peer": true,
       "dependencies": {
         "pg-connection-string": "^2.14.0",
         "pg-pool": "^3.14.0",
@@ -2637,7 +2635,6 @@
       "resolved": "https://registry.npmjs.org/zod/-/zod-3.25.76.tgz",
       "integrity": "sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==",
       "license": "MIT",
-      "peer": true,
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
       }