docs(git-sync): remove dangling references to the deleted git-sync-plan doc (PR #119 review)

The implementation spec docs/git-sync-plan.md was removed as completed, but ~44
code comments still cited it as "plan §N". Strip those citations (comments only),
keeping each comment grammatical. The vendored engine's own "SPEC §N" references
point at a different, still-present spec and are left untouched.

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

packages/git-sync/src/lib/index.ts

@@ -8,7 +8,7 @@
  *
  * The REST client, websocket/collab write-path, auth-utils and page-lock from
  * the upstream package are deliberately NOT vendored (the gitmost server writes
- * natively — plan §2.2/§2.3).
+ * natively).
  */
 export {
   serializeDocmostMarkdown,

packages/git-sync/src/lib/markdown-to-prosemirror.ts

@@ -7,7 +7,7 @@
  * (`preprocessCallouts`, `bridgeTaskLists`). The collaboration/websocket
  * write-path (Hocuspocus, Yjs, `ws`, `withPageLock`, `sanitizeForYjs`) that
  * lives in the same upstream file is intentionally NOT vendored — the gitmost
- * server writes page bodies natively through the collab gateway (plan §3.3).
+ * server writes page bodies natively through the collab gateway.
  */
 import { generateJSON } from "@tiptap/html";
 import { JSDOM } from "jsdom";