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>

Client/udpstreamer/static/calibration.js

@@ -17,7 +17,7 @@
   function baseSignalName(name) {
     var s = String(name == null ? '' : name);
     var open = s.lastIndexOf('[');
-    if (open > 0 && s.charAt(s.length - 1) === ']') {
+    if (open >= 0 && s.charAt(s.length - 1) === ']') {
       var idx = s.slice(open + 1, s.length - 1);
       if (idx.length > 0 && /^[0-9]+$/.test(idx)) return s.slice(0, open);
     }