sync(openai): add embeddings, 4o-image, and tasks integration guides

[Copilot]

Upstream Docs added three new OpenAI service guides not yet reflected in this repo. Syncs openai/ to match the current Docs state.

New guides

• openai_embeddings_api_integration_guide.md — covers the /openai/embeddings endpoint: model selection, dimensions/encoding_format optional params, response shape, error handling.
• openai_chat_completions_4o_image_api_integration_guide.md — covers gpt-4o-image via /openai/chat/completions: reference-image stylization, text-to-image, and multi-image fusion scenarios.
• openai_tasks_api_integration_guide.md — covers /openai/tasks for querying async callback-mode image jobs via retrieve (by id/trace_id) and retrieve_batch (by ids, trace_ids, application_id, user_id, or time window). Includes a full submit-then-poll example and a note that the Tasks API itself is not billed.

README table (openai/README.md)

• Fixed the embeddings row title (was an unresolved i18n key $t(document_title_openai_embeddings_api))
• Added rows for Chat Completion 4o Image API and Tasks API

[acedatacloud-dev]

Auto-closed during PR backlog cleanup: superseded sync (+616/-2) — content covered by next dispatch against current Docs. Root cause was a broken auto-merge in sync-from-docs.yml (now fixed in PR #143). The fix lands a pre-cleanup step + reliable completion signal so future dispatches will not leak PRs. If this PR contained content not yet in main, the next docs-updated dispatch will re-create it via the working pipeline.