sync(openai): add gpt-image-2 docs section, add gpt-5.5/gpt-5.5-pro to model matrix

[Copilot]

Upstream Docs (commit 1ae9499) added gpt-image-2 showcase content and new gpt-5.5/gpt-5.5-pro models to the OpenAI service. This PR brings the openai/ subdirectory in sync.

openai/docs/openai_images_generations_api_integration_guide.md

• Intro paragraph updated: was DALL-E 3 only; now covers dall-e-3, gpt-image-1, and gpt-image-2
• New ## GPT-Image-2 Model section added (was present in upstream, missing here), including:
  • Capability summary (instruction following, text rendering, style range, native aspect ratios)
  • 4 annotated demo scenarios with Python snippets and sample responses:
    • Cinematic portrait (35mm film style, 1024x1536)
    • Vintage travel poster (Art Deco, tests text rendering)
    • Complex composition and counting (1/3/7 books on shelves)
    • Watercolor illustration (landscape 1536x1024)
  • Async/callback timing note (60–90 s per call)

openai/README.md

• GPT-5.x Series model matrix: added gpt-5.5 and gpt-5.5-pro tags, matching the updated openapi/openai.json enum
• Updated card description from "5.1, 5.2, and 5.4" → "5.1, 5.2, 5.4, and 5.5"

[acedatacloud-dev]

Auto-closed during PR backlog cleanup: superseded sync (+121/-3) — content covered by next dispatch against current Docs.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.