Add translations for the "Page already exists (stale list)" and
"Failed to list after retries" messages introduced in the wiki
sync reliability fix.
DEVX-115
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Two failure modes caused post-merge sync-wiki to fail:
1. list_wiki_pages timed out (30s) after 3 retries → aborted sync.
The Gitea wiki API renders pages on each request and can be slow
under load. Increased retries from 3 to 5 with longer backoff
(max 16s). The initial list now uses _list_wiki_pages_with_retry
instead of the raw list_wiki_pages call.
2. After a timeout-retry, list_wiki_pages returned incomplete data.
sync_page tried to CREATE a page that already existed → HTTP 400.
Added a create→update fallback: on HTTP 400 "already exists",
re-list the wiki and PATCH the page instead of failing.
Also added concurrency group to post-merge.yml sync-wiki job to
prevent overlapping runs from conflicting.
DEVX-34
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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>