build(git-sync): land the @docmost/git-sync package into develop, code-only (#326 step 1 / PR-A)

The git-sync converter + engine source lived only on the #119 branch; develop
had just the dead compiled build/. Bring the whole package (src + ~700 tests)
onto develop under CI, with NO consumer wired — git-sync stays fully inert in
develop (nothing in apps/server imports it), so runtime behavior is unchanged.
This unblocks #293 (extract the shared converter package from the landed source)
and lets #119's functionality land LAST, already writing the canonical format
(per the #326 landing order).

- packages/git-sync: src (lib converter + engine) + test corpus + configs.
- Remove develop's dead committed packages/git-sync/build/; gitignore it
  (built in CI/Docker via pnpm build, never committed — no src/build drift).
- pnpm-lock.yaml: add the @docmost/git-sync importer (a missing workspace
  package in the lock is a CI blocker). `pnpm install --frozen-lockfile` passes.
- NO server integration / loader / Dockerfile runtime changes (those come with
  #119 at step 6).

Verified: tsc clean; vitest 711 passed | 1 expected-fail, 0 failures, 0 type
errors; pnpm --frozen-lockfile EXIT 0; apps/server has no git-sync import.

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

packages/git-sync/package.json

@@ -0,0 +1,44 @@
+{
+  "name": "@docmost/git-sync",
+  "version": "0.1.0",
+  "description": "Pure converter + pure sync engine for the Docmost <-> git Markdown sync. See docs/backlog/git-sync-thin-meta.md.",
+  "private": true,
+  "type": "module",
+  "main": "./build/index.js",
+  "types": "./build/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./build/index.d.ts",
+      "default": "./build/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "watch": "tsc --watch",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "license": "MIT",
+  "dependencies": {
+    "@tiptap/core": "3.20.4",
+    "@tiptap/extension-highlight": "3.20.4",
+    "@tiptap/extension-image": "3.20.4",
+    "@tiptap/extension-subscript": "3.20.4",
+    "@tiptap/extension-superscript": "3.20.4",
+    "@tiptap/extension-task-item": "3.20.4",
+    "@tiptap/extension-task-list": "3.20.4",
+    "@tiptap/html": "3.20.4",
+    "@tiptap/pm": "3.20.4",
+    "@tiptap/starter-kit": "3.20.4",
+    "jsdom": "25.0.0",
+    "marked": "17.0.5",
+    "zod": "4.3.6"
+  },
+  "devDependencies": {
+    "@types/jsdom": "^21.1.7",
+    "@types/node": "^20.0.0",
+    "fast-check": "^4.8.0",
+    "typescript": "^5.0.0",
+    "vitest": "4.1.6"
+  }
+}