[Docs] README advertises φ-accrual failure detection as a shipped cluster capability, but the cluster always runs the simple elapsed-time detector

[pathosDev]

Where

• README.md → line 57, the Cluster bullet in the feature list
• docs/src/content/docs/cluster/failure-detector.mdx → "Custom failure detector"
• docs/src/content/docs/de/cluster/failure-detector.mdx → same section

What's wrong

README.md:57 advertises φ-accrual failure detection as a shipped Cluster capability:

• Cluster — gossip membership, φ-accrual failure detection, split-brain

The docs contradict this directly. cluster/failure-detector.mdx states:

The cluster's built-in detector is intentionally simple — plain elapsed-time
thresholds, no statistical variance tracking.

and, about PhiAccrualFailureDetector:

It's not yet wired into the cluster as a selectable detector — the cluster
always runs the simple FailureDetector — so for now you use it standalone.

The code agrees with the docs, not the README. PhiAccrualFailureDetector appears
only in its own definition files and the export barrel:

src/cluster/PhiAccrualFailureDetector.ts   (definition)
src/cluster/PhiAccrualOptions.ts           (definition)
src/cluster/index.ts:77-81                 (re-export only)
src/cluster/Constants.ts:24                (a comment mentioning it)

Nothing in src/cluster/ constructs or consults it on the membership path.

So the README overstates a headline capability of a pre-1.0 framework: a reader
evaluating actor-ts for a partition-sensitive deployment is told the adaptive
detector is in the box, and only discovers on page three of the docs that the
cluster always runs fixed elapsed-time thresholds.

Suggested fix

Make the README bullet match reality, e.g.:

• Cluster — gossip membership, failure detection (φ-accrual detector
  available standalone), split-brain

Both language mirrors of failure-detector.mdx are already correct and need no
change — this is a README-only fix, plus whatever wording keeps the two in step.

Kind

Factually wrong

Notes

• Related but distinct from [Feature] Wire the phi-accrual failure detector options into config #840 (Wire the phi-accrual failure detector options
  into config), which tracks actually doing the wiring. This issue is only that
  the README claims the work is already done. Closing [Feature] Wire the phi-accrual failure detector options into config #840 would make the current
  README sentence true; until then it is not.
• Found by a full-repo knowledge-graph extraction that flagged the README ↔ docs
  edge as AMBIGUOUS; verified by hand against src/.