Consolidate ANSI output sanitization after the ESM migration

Context

Commit 26f051e8 fixes raw ANSI/VT control characters in Local Quick Start Docker logs without adding a dependency:

• Local Quick Start requests colorless output with NO_COLOR=1 and TERM=dumb.
• Output is defensively sanitized with Node's stripVTControlCharacters before it reaches the plain-text VS Code OutputChannel.
• The playground result formatter still has a separate, SGR-only regular expression.

We deliberately avoided adding strip-ansi while the extension is CommonJS. Its current release line is ESM-only, and the CommonJS-compatible 6.x line would be a new dependency on an older release.

Follow-up

After #687 migrates the extension from CommonJS to ESM:

• Review all non-terminal output surfaces that may receive ANSI/VT sequences.
• Consolidate the Local Quick Start and playground sanitizers behind one shared utility.
• Decide whether Node's built-in sanitizer remains sufficient or an ESM-native dependency provides useful behavior.
• Keep terminal/PTY surfaces unchanged, since they should continue interpreting ANSI formatting.
• Add shared regression coverage for SGR sequences and other supported VT controls.

Related: #687

After #687, review commit 26f051e8 and inspect the Local Quick Start and playground output paths for their existing sanitizers. Compare Node's stripVTControlCharacters with the playground's SGR-only expression, then add shared regression coverage for SGR and other supported VT controls while leaving terminal/PTY surfaces unchanged.