refactor: extract devcontainer and harness into separate repos

- Removed .claude/ (skills, agents, rules, hooks, settings) -> stranma/claude-code-harness
- Removed .devcontainer/ (Dockerfile, firewall, devcontainer.json) -> stranma/claude-code-devcontainer
- Removed security hooks and tests (dangerous-actions-blocker, permissions, firewall tamper)
- Removed AGENTS.md (duplicate), docs/DECISIONS.md, docs/DEVELOPMENT_PROCESS.md
- Slimmed CLAUDE.md to template-only dev commands
- Added .ruff_cache/, .agents/, .tmp_*/ to .gitignore
- 15 template tests still pass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stranma