feat(core): add pinned Code Mode tools

[rekram1-node]

Summary

• add pinned registration metadata for Code Mode tools
• reject pinned: true when codemode: false
• keep pinned signatures visible when compact catalog budgeting hides ordinary listings
• filter permissions before pinned catalog rendering and keep false/default metadata absent
• document the plugin registration option

Testing

• bun test test/codemode.test.ts test/codemode/catalog.test.ts test/session-runner-tool-registry.test.ts in packages/core (37 passed)
• bun test test/tool.test.ts in packages/plugin (6 passed)
• bun typecheck in packages/core and packages/plugin
• bun validate in packages/docs
• Prettier and git diff --check
• independent subagent audit