fix(plh): require CLAUDE.md commands/agents/hooks section only for shipped components

plugin-health flagged "CLAUDE.md missing <commands|agents|hooks> section" regardless of
whether the plugin actually had that component — e.g. graceful-handoff (no commands/ or
agents/ dir) got two spurious medium findings. Same over-report class as the model-field fix.

Now gated on component presence (pluginShipsComponent): a section is required only if the
plugin ships that component (commands/ or agents/ with .md, or hooks/hooks.json). Across the 5
stable plugins this drops 12 spurious findings to 3 legitimate ones (graceful-handoff hooks,
ai-psychosis commands+hooks). New fixture plugin-section-coverage proves both directions.
Found via the marketplace-wide review. Suite 950/950, self-audit A/A, scanner count 13.
tests badge 949 -> 950.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

tests/fixtures/plugin-section-coverage/.claude-plugin/plugin.json

@@ -0,0 +1,5 @@
+{
+  "name": "section-coverage",
+  "description": "Fixture: ships one command, no agents or hooks",
+  "version": "1.0.0"
+}

tests/fixtures/plugin-section-coverage/CLAUDE.md

@@ -0,0 +1,7 @@
+# Section Coverage Fixture
+
+## Overview
+
+This plugin ships one command and no agents or hooks. Its CLAUDE.md intentionally omits the
+Commands section, so the missing-section check should fire for `commands` (a component it has)
+but NOT for `agents` or `hooks` (components it does not have).

tests/fixtures/plugin-section-coverage/commands/foo.md

@@ -0,0 +1,7 @@
+---
+description: A demo command for the section-coverage fixture
+---
+
+# Foo
+
+Demo command body.