docs: update README supported models and engine classes

[jadenfix]

Summary

• Sync the README Supported Models and Engine Classes tables with the backend source of truth (roe-llm AIModel enum + DEPRECATED_MODELS, and roe-agents prod_workflow_types / migrated_workflow_types).
• Add current models that were missing: GPT-5.5 Pro (gpt-5.5-pro-2026-04-23), GPT-5.5 (gpt-5.5-2026-04-23), Claude Opus 4.8 (claude-opus-4-8).
• Remove deprecated engine IDs and replace with their current equivalents:
  • PerplexitySearchEngine → ResearchEngine
  • LinkedInScraperEngine dropped (migrated to SocialScraperEngine, already listed)
  • Added MarketplaceStorefrontAnalysisEngine (current prod engine that was missing)

Tenant-restricted models (SageMaker, StateStreet power-proxy/azure/dbs) are intentionally excluded, matching the public discovery endpoint's filtering.

Test plan

• Verified every listed model ID is non-deprecated in roe-llm/src/roe_llm/defs.py
• Verified every listed engine ID is in roe-agents/src/lib/temporal_processing/utils.py prod_workflow_types and absent from migrated_workflow_types
• Docs-only change — render check on GitHub

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR updates the README's Supported Models and Engine Classes reference tables to match the backend source of truth. It adds three new models and synchronizes the engine list by replacing deprecated entries with their current equivalents.

• Models added: GPT-5.5 Pro (gpt-5.5-pro-2026-04-23), GPT-5.5 (gpt-5.5-2026-04-23), and Claude Opus 4.8 (claude-opus-4-8), inserted in descending version order consistent with existing entries.
• Engines updated: PerplexitySearchEngine replaced by ResearchEngine, LinkedInScraperEngine removed (already superseded by SocialScraperEngine), and MarketplaceStorefrontAnalysisEngine added as a previously missing prod engine.

Confidence Score: 5/5

Safe to merge — purely additive documentation changes with no logic, runtime, or API contract modifications.

Only README.md is touched. The additions (three models, one new engine) follow the established formatting conventions and ordering. The removals (PerplexitySearchEngine, LinkedInScraperEngine) are consistent with the stated deprecation status in the backend source. No functional code is altered.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Documentation-only update adding GPT-5.5 Pro/GPT-5.5/Claude Opus 4.8 models, replacing PerplexitySearchEngine with ResearchEngine, dropping LinkedInScraperEngine, and adding MarketplaceStorefrontAnalysisEngine

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