feat(claude-ops): inventory lane for built-in cc-plugin-* plugins #5733

Problem

The Claude Code binary registers built-in plugins (cc-plugin-*@builtin). On 2.1.287 a string search finds mods-guide, tips, mermaid, responsive-mode, diff, you-should-know and claude-test; the 2.1.287 changelog announces cc-plugin-you-should-know@builtin and Claude Mods. They were already present in 2.1.286. No inventory lane covers them: plugin_backed holds only security-review. The native-surface registry and overlap detection therefore cannot see their skills, commands or agents.

Fix

Add a builtin_plugins lane to plugins/claude-ops/skills/inventory/scripts/inventory.py that extracts each built-in plugin's name, enabled/gated state, and its components (skills, commands, agents, hooks), read from the binary by string literal, fail-closed like the other lanes. Feed the components to overlap.py detect so they get rulings, and add the lane to --self-check and reference/extraction.md.

Acceptance

• On 2.1.287 the lane lists every cc-plugin-* the binary registers, with components; 2.1.285/2.1.286 outputs for existing lanes unchanged.
• --self-check covers the lane; detect rules or dismisses every new candidate.
• Synthetic-fixture tests for the extraction.

Found by the 2.1.287 per-release pass (#5731). Related: #5640 (JS parser for the bundle reader).