Add token-optimizer skill/plugin

[TheNew000]

Adds token-optimizer, a skill that generates and maintains a per-repo architecture map (.claude/codebase-overview.md) so agents skip exploratory file reading on unfamiliar codebases.

Installable two ways:

• Skill only (via Skills CLI): architecture-map generation.
• Plugin (recommended): adds an explorer subagent that routes verbose work to Haiku, a PreToolUse hook that filters test output to failures-only, and a /token-optimizer:setup command that bootstraps a repo with a lean CLAUDE.md.

Also registers the plugin in .claude-plugin/marketplace.json and documents the skill-vs-plugin tradeoff in the README.