Revisit provisional design decisions once used in production

[NewerKey]

The README's "Status & contributing" section already flags these as
judgment calls made with the information available at the time, not
settled conclusions. Filing so they don't get silently forgotten once
real usage feedback (from adopting a new adapter, or actual production
use) comes in:

• TTL default in WorkflowStateManager (state.py) — is the
  current default right for real commit→deploy gaps, or too
  aggressive/lax?
• Closed EventType enum (schema.py) — does it need to open up
  once a tool with a genuinely different lifecycle stage shows up (e.g.
  via a new adapter from Add more source adapters (Linear, Azure DevOps, Jenkins, CircleCI, Bitbucket) #1)?
• Dropped CORRELATION_STRATEGY toggle — idp-observ had a
  fallback-to-random-IDs escape hatch; keythread deliberately removed
  it. Revisit if a real deployment ever needs it.

No action needed until one of these actually causes friction — this
issue exists so "later" has a home instead of living only in a chat
transcript.