test(visual-ide): add unit tests for stdoutParser.js marker formats

[ax1s-x1zz]

Summary

The visual IDE (visual-ide/) has a stdout marker parser (src/transpiler/stdoutParser.js) that parses [xazz:*] markers, but there is no unit test for it, and the contract tests (visual-ide/tests/contract.mjs) don't cover the parser. Recently the [xazz:chart] and [xazz:dp] markers changed from a two-line format to a single-line self-contained format (with the old two-line form kept as a fallback). This is untested and worth locking down.

Context

• Parser: visual-ide/src/transpiler/stdoutParser.js — parseStdout(lines) returns ExecutionEvent[]; helpers getChartEvents, getErrorEvents, getTextEvents.
• New single-line formats:
  • [xazz:chart] {JSON} (and legacy: [xazz:chart] then JSON on next line)
  • [xazz:dp] {JSON}
• The repo has no JS test runner for this file (no vitest/jest configured). visual-ide/package.json scripts use node tests/*.mjs for contract tests.

Task

Add a lightweight test harness for stdoutParser.js:

1. A visual-ide/tests/stdoutParser.mjs (plain Node, no new deps) that imports parseStdout from the transpiler and asserts:
   • single-line [xazz:chart] {json} produces a chart event with transformed data (bar/line with x/y; pie with label/value).
   • legacy two-line [xazz:chart] + JSON still parses (fallback).
   • [xazz:dp] {json} is ignored as a text/unknown event (the parser doesn't emit dp events — assert it doesn't crash and yields a text event).
   • [xazz:result] {json} yields a text event (current behavior).
   • [xazz:error] + AI_SUGGESTION: legacy block yields an error event with suggestion.
   • random/non-marker lines yield text events.
2. Wire it into package.json as "test:stdout": "node tests/stdoutParser.mjs".
3. Document in the test file how to run it.

Definition of Done

• cd visual-ide && npm run test:stdout passes (requires no server, no browser).
• The existing npm run build still works.
• Assertions cover both the new single-line and legacy two-line marker forms.

Notes

• Pure JS, no React/DOM — can run in plain Node with the ESM import.
• Do not rename or restructure parseStdout; only add tests (fix any bug you find, but note it clearly in the PR).