Migrate LLM provider + sanitize to cortex

[yuzi-co]

Context

omkit.provider (ProviderBase, ProviderRegistry) and omkit.sanitize (sanitize_llm_output, sanitize_llm_response, extract_json) are LLM-specific concerns. LLM abstraction belongs in cortex (within the omur platform), not in the multi-tenant scaffolding kit.

Keeping them in omkit:

• bloats the surface area for services that don't talk to LLMs
• forces version-locking the LLM abstraction to omkit releases
• competes with LiteLLM / LangChain / Vercel AI SDK on a fight omkit shouldn't pick

Plan

1. Inventory all internal consumers of omkit.provider and omkit.sanitize
2. Land the equivalent surface in cortex (LLM provider registry + LLM-output sanitizers)
3. Mark omkit.provider + omkit.sanitize as deprecated shims that re-export from cortex (one release)
4. Remove from omkit in the following major
5. Update omkit.security facade — strip sanitize re-exports, keep log_security_event

Acceptance

• Cortex provides provider + LLM-output sanitizers
• omkit modules become deprecation shims with DeprecationWarning
• README + module index reflect removal
• Downstream services migrated

Related

• omurlabs/omkit-go: paired removal of provider package