fix: address all 9 findings from final calibration code review

- calibration.js: fix baseSignalName('[0]') parity with Go/C++ (>= 0 not > 0)
- calibration.test.js: add assertions for '[0]' edge case in two existing tests
- app.js: remove stale typeof guard around refreshVScaleMenu (always defined)
- app.js: call refreshTrigThresholdField on trig-signal change (both assignment sites)
- index.html: drop maxlength='16' on unit input; normaliseCal is the sole enforcer
- configcheck/main.go: delete dead nextOneOf function (no callers)
- hub_calibration_test.go: delete orphaned waitBroadcast comment (function never existed)
- calibration.go: correct arrayIndexSuffix comment to document known Go/C++ difference
- Docs/StreamHub-API.md: add calibration entry count and unit byte limits to §5 table
- spec: fix configReloaded missing path field, '16 chars'→'16 UTF-8 bytes', StreamString→char[], chain scenario→configcheck program, four→five new frames

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Common/Client/go/wshub/hub_calibration_test.go

@@ -129,8 +129,4 @@ func waitMsg(t *testing.T, sendCh chan wsMessage, msgType string) []byte {
 	}
 }
 
-// waitBroadcast is kept for compatibility with the test helper interface;
-// it delegates to waitMsg using a pre-registered client send channel.
-// Callers that need it should register a client and use waitMsg directly.
-
 func sleepMillis(n int) { time.Sleep(time.Duration(n) * time.Millisecond) }