sync(openai): remove gpt-image-1.5, add gpt-image-2 size/billing table

[Copilot]

Upstream Docs removed gpt-image-1.5 and added new gpt-image-2 resolution tiers and billing information. Syncs the two affected guide files accordingly.

openai_images_generations_api_integration_guide.md

• Drop gpt-image-1.5 from description and conclusion
• Update GPT-Image-2 feature bullet: 3 hardcoded sizes → 5 aspect ratios × 3 resolution tiers (1K/2K/4K)
• Add Supported size Values and Billing Tiers section with the full 15-size table; 2K/4K billed at 1.5× 1K rate
• Update Scenario 4 illustration URL to match upstream

openai_images_edits_api_integration_guide.md

• Drop gpt-image-1.5 from description and basic-usage conclusion
• Add 4th GPT-Image-2 bullet: high-resolution redrawing (pass 1K source, request 2K/4K output)
• Add same Supported size Values and Billing Tiers table; billing based on requested size, not source resolution

[acedatacloud-dev]

Auto-closed during PR backlog cleanup: superseded sync (+39/-6) — content covered by next dispatch against current Docs.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.