Add session entries to progress logs, update CLAUDE.md files with
rule 18 reference and rem units, archive multi-machine progress
entries, update CHANGELOG/TODO/v3-task_plan with CSS units decision.
- Added pathToClaudeCodeExecutable and findClaudeCli() docs to CLAUDE.md,
.claude/CLAUDE.md, task_plan.md decisions log, and CHANGELOG.md
- Split docs/progress.md (425 lines) into progress.md (153 lines) +
progress-archive.md (180 lines) to stay under 300-line threshold
- Updated docs/README.md, README.md with archive file reference
- Updated TODO.md with completed items from this session
