chore(consumer): drop dead CircuitBreakerController.shouldProbe + fix docs

[eschizoid]

Summary

Two-part cleanup surfaced by the CircuitBreaker wiring investigation that ran alongside #186–#188:

1. Delete the stranded CircuitBreakerController.shouldProbe(long, long) helper and its two unit tests. Audit found zero production callers. The Javadoc claimed "a timer asks shouldProbe on each tick" — but no such tick exists in production. The real OPEN → HALF_OPEN transition fires via scheduler.schedule(this::tryHalfOpen, openDuration, …) in ConsumerHealthController.trip(), so the delay itself encodes the threshold (no predicate, no polling).
2. Rewrite the class Javadoc's OPEN-state description to describe the actual one-shot-scheduler design.
3. Add a "Circuit breaker" row to the §17 capability table in .claude/CLAUDE.md — the table was missing it entirely, despite the feature being public on both the fluent facade (Stream.withCircuitBreaker(...) / MultiBuilder.withCircuitBreaker(...)) and the explicit Builder (Builder.withCircuitBreaker(CircuitBreakerController)).

Why this is safe

The investigation explicitly verified:

• shouldProbe callers in production: zero. Test-only callers: 4 assertions across 2 test methods, both in CircuitBreakerControllerTest.
• recordOutcome callers in production: KPipeConsumer.java:1647 (success path) + KPipeConsumer.java:1765 (failure path). The full circuit-breaker pause path is wired and exercised by KPipeCircuitBreakerIntegrationTest.

This PR only touches the helper, not the wiring.

Test plan

• ./gradlew :lib:kpipe-consumer:test --tests "*CircuitBreaker*" → BUILD SUCCESSFUL
• Merge to main
• KPipeCircuitBreakerIntegrationTest continues to pass on next push

[eschizoid]

@copilot please review

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.06%. Comparing base (165b5dc) to head (0e4aaa4).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #189      +/-   ##
============================================
- Coverage     77.08%   77.06%   -0.02%     
+ Complexity      752      749       -3     
============================================
  Files            72       72              
  Lines          2858     2856       -2     
  Branches        355      354       -1     
============================================
- Hits           2203     2201       -2     
  Misses          489      489              
  Partials        166      166              

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