feat: add parsimony plugin for token efficiency

[jm-cnaught]

Summary

• Adds parsimony plugin — a token efficiency skill that reduces controllable token usage by ~30% and speeds up responses by ~48% without sacrificing output quality
• Includes skill (SKILL.md), two slash commands (/token-mode, /token-report), plugin manifest, and README with benchmark results
• Registers parsimony in marketplace.json alongside the existing carbon plugin

What's included

File	Purpose
plugins/parsimony/skills/parsimony/SKILL.md	Core skill — tool rules, response rules, planning friction, token ledger
plugins/parsimony/commands/token-mode.md	/token-mode <efficient|ultra|off> slash command
plugins/parsimony/commands/token-report.md	/token-report savings summary slash command
plugins/parsimony/.claude-plugin/plugin.json	Plugin manifest
plugins/parsimony/README.md	Install instructions, modes, benchmarks
.claude-plugin/marketplace.json	Updated to register parsimony
README.md	Updated with parsimony in Plugins section

Benchmark results (Opus, controllable tokens only)

Task	Savings	Speed Gain
Summarize large file	80.9%	43% faster
Write TypeScript module	55.4%	58% faster
Debug Python function	34.6%	52% faster
Refactor JavaScript	19.3%	66% faster
Search/list files	17.1%	39% faster
Compare two files	4.4%	32% faster
Average	30.0%	~48% faster

Test plan

• Install plugin via claude plugin install parsimony --marketplace cnaught-plugins
• Verify skill loads and applies token-efficient behavior by default
• Test /token-mode ultra and /token-mode off switching
• Test /token-report output format
• Verify no regressions in carbon plugin

🤖 Generated with Claude Code