refactor(git-sync): address PR #119 review #3 — honest gitRemote scaffolding comments, env example, shared ESM bridge

1. gitRemote is NOT yet consumed (the vendored engine has no remote-push path,
   SPEC §7). Corrected the buildSettings docstring (it wrongly called gitRemote
   "load-bearing") and marked the env -> validation -> getter -> buildSettings
   chain as inert SCAFFOLDING for the deferred remote-push feature at all three
   sites. Kept the wiring (harmless; removing only churns).

2. .env.example: document that GIT_SYNC_REMOTE_TEMPLATE substitutes the literal
   "{spaceId}" per-space (with the example), so an operator doesn't point every
   space at one remote.

3. Extracted the copy-pasted CJS->ESM dynamic-import bridge
   (`new Function('s','return import(s)')`) into one shared
   common/helpers/esm-import.ts; git-sync.loader, docmost-client.loader and
   mcp.service now import it and keep their own typed loadX() wrappers.

Deferred (notes only, not implemented):
- lcs.ts + three-way-merge.ts could move into packages/git-sync, but that engine
  is vendored (manual re-sync) — added a one-line note at three-way-merge.ts to
  revisit once the re-sync story is settled.
- schema-core single source + BullMQ/fencing remain documented from prior rounds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/integrations/git-sync/git-sync.loader.ts

@@ -1,4 +1,5 @@
 import { pathToFileURL } from 'node:url';
+import { esmImport } from '../../common/helpers/esm-import';
 import type {
   VaultGit as VaultGitClass,
   vaultGitEnv as vaultGitEnvFn,
@@ -21,16 +22,9 @@ interface GitSyncModule {
   markdownToProseMirror: typeof markdownToProseMirrorFn;
 }
 
-// TS with module:commonjs downlevels a literal `import()` to `require()`, which
-// cannot load the ESM-only `@docmost/git-sync` package. Indirect through
-// Function so the real dynamic `import()` survives compilation and can load ESM
-// from CommonJS at runtime (same trick as
-// apps/server/src/core/ai-chat/tools/docmost-client.loader.ts and
-// integrations/mcp/mcp.service.ts).
-const esmImport = new Function(
-  'specifier',
-  'return import(specifier)',
-) as (specifier: string) => Promise<unknown>;
+// The CJS->ESM dynamic-import bridge lives in one shared helper
+// (common/helpers/esm-import.ts); see it for why `import()` must be hidden from
+// the TS commonjs downleveler. The typed `loadGitSync()` wrapper stays here.
 
 // Memoize the in-flight/loaded module so the dynamic import runs at most once.
 let modulePromise: Promise<GitSyncModule> | null = null;