test(humanizer): replace title-string assertions with ID-based checks

Wave 2 / Step 4 of v5.1.0 plain-language UX humanizer rollout. Re-anchors
34 title-string assertions across 4 test files so they survive Wave 3's
title/description/recommendation rewriting at the CLI layer.

Anchoring strategy per scanner:
- GAP findings: scanner + category + recommendation substring (humanizer
  preserves stable identifiers like CLAUDE.md, .mcp.json, hook in rec).
  Hardcoded CA-GAP-NNN IDs for positive checks.
- HKV findings: scanner + evidence regex (evidence preserved verbatim).
- SET findings: scanner + evidence regex (evidence preserved verbatim).
- PLH findings: scanner + hardcoded CA-PLH-NNN IDs (no evidence on most
  PLH findings, so ID is the only stable anchor for specific cases;
  negative checks use scanner + title-substring spanning raw + humanized).

Per docs/v5.1.0-test-audit.md classification: only (b) WILL BREAK
assertions modified. (a) shape-only assertions (error-message formatting,
pure existence checks) untouched. tests/lib/output.test.mjs and
tests/lib/diff-engine.test.mjs and tests/scanners/fix-engine.test.mjs
unchanged (synthetic test inputs, not scanner output).

Test count unchanged: 689/689 pass. IDs harvested via deterministic
runtime dump per fixture (resetCounter + scan).

plugins/config-audit/tests/scanners/plugin-health-scanner.test.mjs

@@ -49,14 +49,21 @@ describe('scan on valid test-plugin', () => {
   it('no findings for missing plugin.json fields', async () => {
     resetCounter();
     const result = await scan(TEST_PLUGIN);
-    const missingFields = result.findings.filter(f => f.title.includes('Missing required field'));
+    // Anchor on PLH + a title-substring stable across humanizer rewrites.
+    // Raw: "Missing required field in plugin.json: <field>". Humanized: "A plugin's manifest is missing a required field".
+    const missingFields = result.findings.filter(f =>
+      f.scanner === 'PLH' && /(missing.{0,40}(field|manifest))|(manifest.{0,40}missing)/i.test(f.title || '')
+    );
     assert.equal(missingFields.length, 0, 'All required fields present in test-plugin');
   });
 
   it('no findings for missing CLAUDE.md sections', async () => {
     resetCounter();
     const result = await scan(TEST_PLUGIN);
-    const missingSections = result.findings.filter(f => f.title.includes('missing') && f.title.includes('section'));
+    // Raw: "CLAUDE.md missing '<name>' section". Humanized: "A plugin's instructions file is missing a recommended section".
+    const missingSections = result.findings.filter(f =>
+      f.scanner === 'PLH' && /missing.{0,40}section/i.test(f.title || '')
+    );
     assert.equal(missingSections.length, 0, 'All sections present in test-plugin CLAUDE.md');
   });
 });
@@ -65,32 +72,38 @@ describe('scan on broken-plugin', () => {
   it('detects missing plugin.json fields', async () => {
     resetCounter();
     const result = await scan(BROKEN_PLUGIN);
-    const missingFields = result.findings.filter(f => f.title.includes('Missing required field'));
+    // CA-PLH-001 (description) and CA-PLH-002 (version) in broken-plugin.
+    const missingFields = result.findings.filter(f =>
+      f.scanner === 'PLH' && (f.id === 'CA-PLH-001' || f.id === 'CA-PLH-002')
+    );
     assert.ok(missingFields.length >= 2, 'Should detect missing description and version');
   });
 
   it('detects missing CLAUDE.md', async () => {
     resetCounter();
     const result = await scan(BROKEN_PLUGIN);
-    const missingMd = result.findings.filter(f => f.title === 'Missing CLAUDE.md');
+    // CA-PLH-003 in broken-plugin = Missing CLAUDE.md.
+    const missingMd = result.findings.filter(f => f.scanner === 'PLH' && f.id === 'CA-PLH-003');
     assert.equal(missingMd.length, 1, 'Should detect missing CLAUDE.md');
   });
 
   it('detects command without frontmatter', async () => {
     resetCounter();
     const result = await scan(BROKEN_PLUGIN);
-    const noFrontmatter = result.findings.filter(f => f.title === 'Command missing frontmatter');
+    // CA-PLH-004 in broken-plugin = Command missing frontmatter.
+    const noFrontmatter = result.findings.filter(f => f.scanner === 'PLH' && f.id === 'CA-PLH-004');
     assert.equal(noFrontmatter.length, 1, 'Should detect command without frontmatter');
   });
 
   it('detects agent missing required frontmatter fields', 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.title.startsWith('Agent missing frontmatter field:')
+      f.scanner === 'PLH' && (f.id === 'CA-PLH-005' || f.id === 'CA-PLH-006')
     );
     // 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.title).join(', ')}`);
+    assert.ok(missingAgent.length >= 2, `Should detect missing model and tools, got ${missingAgent.length}: ${missingAgent.map(f => f.id).join(', ')}`);
   });
 });
 
@@ -99,7 +112,9 @@ describe('scan with no plugins', () => {
     resetCounter();
     const result = await scan(resolve(FIXTURES, 'empty-project'));
     assert.equal(result.findings.length, 1);
-    assert.equal(result.findings[0].title, 'No plugins found');
+    // CA-PLH-001 in empty-project = No plugins found.
+    assert.equal(result.findings[0].id, 'CA-PLH-001');
+    assert.equal(result.findings[0].scanner, 'PLH');
     assert.equal(result.findings[0].severity, 'info');
   });
 });