fix(plh): align required-frontmatter with CC docs (drop optional model/tools/name)

plugin-health-scanner required `model`+`allowed-tools` on commands and `model`+`tools`
on agents, plus `name` on commands. Per primary docs these are OPTIONAL:
- Commands/skills (code.claude.com/docs slash-commands): "All fields are optional. Only
  `description` is recommended." `name` defaults to the directory name.
- Subagents (code.claude.com/docs sub-agents): "Only `name` and `description` are required";
  `model` defaults to `inherit`, `tools` inherits all.

REQUIRED_COMMAND_FRONTMATTER -> [description]; REQUIRED_AGENT_FRONTMATTER -> [name, description].
This was over-reporting: every command without an explicit `model` got a spurious medium
finding (10 on the okr plugin alone). Found via the okr pilot review. Suite 949/949, self-audit
A/A, scanner count 13 (no new scanner).

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

tests/fixtures/broken-plugin/agents/bad-agent.md

@@ -1,8 +1,8 @@
 ---
 name: bad-agent
-description: Missing model and tools
 ---
 
 # Bad Agent
 
-No model or tools in frontmatter.
+Has a `name` but no `description`. Per CC sub-agents docs, `name` and `description` are
+required for subagents; `model` and `tools` are optional (inherit / all-tools by default).

tests/scanners/plugin-health-scanner.test.mjs

@@ -99,15 +99,17 @@ describe('scan on broken-plugin', () => {
     assert.equal(noFrontmatter.length, 1, 'Should detect command without frontmatter');
   });
 
-  it('detects agent missing required frontmatter fields', async () => {
+  it('flags missing required agent field (description) but not optional model/tools', async () => {
     resetCounter();
     const result = await scan(BROKEN_PLUGIN);
-    // CA-PLH-005 (missing model) and CA-PLH-006 (missing tools) in broken-plugin.
-    const missingAgent = result.findings.filter(f =>
-      f.scanner === 'PLH' && (f.id === 'CA-PLH-005' || f.id === 'CA-PLH-006')
+    // Per CC sub-agents docs: only `name` and `description` are required; `model` and `tools`
+    // are optional (inherit / all-tools by default). bad-agent.md has `name` only.
+    const agentFields = result.findings.filter(f =>
+      f.scanner === 'PLH' && /Agent missing frontmatter field/.test(f.title || '')
     );
-    // bad-agent.md has name+description but missing model and tools
-    assert.ok(missingAgent.length >= 2, `Should detect missing model and tools, got ${missingAgent.length}: ${missingAgent.map(f => f.id).join(', ')}`);
+    assert.ok(agentFields.some(f => /description/.test(f.title)), 'missing required `description` must be flagged');
+    assert.ok(!agentFields.some(f => /\b(model|tools)\b/.test(f.title)),
+      `optional model/tools must not be flagged, got: ${agentFields.map(f => f.title).join('; ')}`);
   });
 });