docs: Add engine version justification to CHANGELOG

Added clarification that VS Code 1.104.0+ is required for modern APIs
and stability improvements. This prevents future audit confusion about
why this specific version is required.

Changes:
- Enhanced CHANGELOG.md line 42 with rationale for engine requirement

Context:
- Counter-audit of false-positive claims revealed need for explicit
  version justification
- CHANGELOG markdown formatting already consistent (all hyphens)
- All 336 tests passing
- No functional changes

Author: JohannesHoppe

CHANGELOG.md

@@ -39,4 +39,4 @@ This extension is a modernized extraction of the "Organize Imports" feature from
 - Native VSCode OutputChannel logging (replaced winston)
 - Modern esbuild bundling (replaced tsc)
 - TypeScript 5.7+ with strict mode
-- VSCode engine 1.104.0+
+- VSCode engine 1.104.0+ (required for modern VS Code APIs and stability improvements)