merge: resolve v1.21.1 conflicts with custom

Resolve all 10 upstream v1.21.1 merge conflicts into custom, keeping
custom's GitLab/Gitea forge customizations layered on upstream while
lifting upstream improvements. Restored tr.ts i18n key parity with the
custom en.ts dictionary (471 custom forge keys added, en fallback) so the
upstream-introduced locale stays in parity.

Also stage bun.lock version alignment (1.21.0 -> 1.21.1) that matches the
staged package.json bump.

Verification: ui + web type-check pass; ui/web tests pass except
pre-existing failures on the custom baseline (forge.test.ts, session-actions,
issue-1637-2270, routes.test.js fs-stat directory scope).

packages/docs/sidebar.config.json

@@ -308,6 +308,21 @@
             "tr": "GitHub issue'ları ve PR'lar"
           }
         },
+        {
+          "label": "GitLab Issues & MRs",
+          "link": "/gitlab/",
+          "translations": {
+            "uk": "Завдання та MR GitLab",
+            "zh-CN": "GitLab 工单与 MR",
+            "es": "Issues y MRs de GitLab",
+            "pt-BR": "Issues e MRs do GitLab",
+            "ko": "GitLab 이슈 및 MR",
+            "pl": "Zgłoszenia i MR-y GitLab",
+            "fr": "Issues et MR GitLab",
+            "ja": "GitLab Issues と MR",
+            "de": "GitLab-Issues und MRs"
+          }
+        },
         {
           "label": "Magic Prompts",
           "link": "/magic-prompts/",