docs(humanizer): v5.1.0 release notes across plugin + marketplace docs

- Plugin README: add "What's New in v5.1.0" section with humanizer overview,
  before/after example, plain-language vocabulary table, --raw flag docs.
  Bump version badge 5.0.0 → 5.1.0. Add Version History row.
- Plugin CLAUDE.md: add humanizer.mjs + humanizer-data.mjs to Scanner Lib
  table. Add "Plain-Language Output (v5.1.0)" section documenting output
  modes, vocabularies, and Wave 5 lessons. Bump test count 635 → 792 across
  52 test files.
- Marketplace root README: bump config-audit entry 5.0.0 → 5.1.0, update
  one-line description to mention plain-language UX, add bullet for the
  v5.1.0 humanizer, bump test count 635+ → 792+.

Test-normalizer hardening (consequence of growing CLAUDE.md):
walkClaudeMdCascade walks upward from the marketplace-medium fixture into
this plugin's own CLAUDE.md, so any docs edit ripples into
`scanners[*].activeConfig.claudeMdEstimatedTokens`. The v5.0.0 byte-stability
contract is about scanner internals being unchanged, not ancestor input
content being frozen. Normalizers in json-backcompat, raw-backcompat,
posture-humanizer, scan-orchestrator-humanizer, and snapshot-default-output
now strip claudeMdEstimatedTokens to <ANCESTOR_DERIVED>. The
default-output snapshot for scan-orchestrator was re-seeded via
UPDATE_SNAPSHOT=1 (intent: Wave 6 docs additions; humanizer prose
unchanged).

Verify:
- grep -E "5\.1\.0|v5\.1\.0" README.md CLAUDE.md ../../README.md | wc -l = 12
- node --test 'tests/**/*.test.mjs' = 792/792 pass
- self-audit configGrade A (97), pluginGrade A (100), readmeCheck.passed true

plugins/config-audit/tests/snapshots/default-output/scan-orchestrator.json

@@ -491,7 +491,7 @@
         ],
         "total_estimated_tokens": 1809,
         "activeConfig": {
-          "claudeMdEstimatedTokens": 5716,
+          "claudeMdEstimatedTokens": "<ANCESTOR_DERIVED>",
           "mcpServerCount": 3,
           "pluginCount": 41,
           "skillCount": 65