Vega charts skill recommends locale-dependent formatDecimal for JSON; run --local query hint ignores the admin port #982

Small items from the JTSBootLogboek project (H17 and side findings), measured on main fcddbc6.

1. The Vega charts skill recommends locale-dependent formatDecimal for JSON.
   • .claude/skills/packs/mendix-vega-charts/SKILL.md:165,170 and specs/README.md:44 say formatDecimal(x, '0.00') "is the right way to write a number into JSON". It follows the user's language, so a Dutch user gets 12,5 and "Data is not valid JSON".
   • Measured on 11.13: formatDecimal(1234.5, '0.00', 'nl-NL') gives 1234,50. The underscore form 'nl_NL' silently falls back to the default.
   • toString(round($x, 2)) gives 12.35, is locale-independent, and uses no exponent even for 0.0000001.
   • Fix the skill to use toString(round($x, 2)), or formatDecimal($x, '0.00', 'en-US') with a hyphenated tag. Explain why. Optionally a lint rule for a locale-less formatDecimal inside JSON-building concatenation.
2. run --local prints a query hint that ignores its own admin port. It prints mxcli oql -p …, which ignores the non-default --admin-port recorded in .mxcli/run-local.json and fails with "cannot connect … localhost:8090". mxcli log has the same issue. Read run-local.json for the admin port and credentials.