fix(git-sync): git-http stream error handlers + close test gaps (#119 review)

Addresses the stability + test-coverage warnings from the #119 review:

- git-http-backend.service.ts: add `'error'` handlers to child.stdout/stderr. An
  EventEmitter 'error' with no listener (e.g. EPIPE when the client aborts
  mid-response) is rethrown by Node as an uncaught exception and crashes the
  process; now swallowed + logged (never echoed to the client).
- TEST INFRA: a jest setupFile shims `navigator`/`MessageChannel` for the `node`
  testEnvironment. react-dom@18 reads `navigator` at module-init (pulled in via
  @docmost/editor-ext -> @tiptap/react), so every spec transitively importing the
  conversion engine — including git-http.service.spec.ts — previously FAILED TO
  LOAD ("navigator is not defined") and ran ZERO tests. With the shim those specs
  now run (git-sync integration: 11 suites / 133 tests green).
- git-http.service.spec.ts: cover the 503 lock-held push path — `ingestExternalPush`
  rejecting `GitSyncLockHeldError` -> 503 + Retry-After + "git-sync busy, retry",
  no double header write (+ the already-headers-sent no-rewrite path).
- git-http-backend.service.spec.ts: unit-test run() — child 'error'/'close' before
  headers -> 500; normal CGI parse+stream; stdout/stderr 'error' (EPIPE) swallowed;
  synchronous spawn throw -> 500.
- page-change.listener.ts: implement OnModuleDestroy to clearTimeout all pending
  debounce timers on shutdown (+ test).
- .env.example: vaults are non-bare working repos, not "bare repos".

(Docs deleted by the stray commit were restored in 9cdbce54.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/test/jest.setup.ts

@@ -0,0 +1,29 @@
+// Jest global setup (runs before each test module loads).
+//
+// react-dom@18 (pulled in transitively via @docmost/editor-ext -> @tiptap/react
+// -> react-dom, e.g. through the math node) reads `navigator` at MODULE-INIT
+// time. The server jest config uses `testEnvironment: "node"`, which has no
+// `navigator`, so ANY spec that transitively imports the editor schema/engine
+// (e.g. the git-sync HTTP service specs, which reach the conversion engine)
+// fails to LOAD with "ReferenceError: navigator is not defined". These specs
+// never exercise the DOM — they just can't survive the import. Provide the
+// minimal browser globals those modules touch at import so the specs run.
+/* eslint-disable @typescript-eslint/no-explicit-any */
+const g = globalThis as any;
+
+if (typeof g.navigator === "undefined") {
+  // react-dom only reads navigator.userAgent at init; keep it minimal.
+  Object.defineProperty(g, "navigator", {
+    value: { userAgent: "node", platform: "node" },
+    configurable: true,
+    writable: true,
+  });
+}
+
+if (typeof g.MessageChannel === "undefined") {
+  // react-dom's scheduler references MessageChannel at init in some builds.
+  g.MessageChannel = class {
+    port1 = { postMessage() {}, close() {}, onmessage: null };
+    port2 = { postMessage() {}, close() {}, onmessage: null };
+  };
+}