feat(eng): add contributor reporting and management scripts

- Add eng/README.md documenting maintainer utilities
- Add eng/contributor-report.mjs for generating contributor reports
- Add eng/add-missing-contributors.mjs for automating contributor additions
- Add eng/utils/graceful-shutdown.mjs for script lifecycle management
- Update eng/update-readme.mjs with minor fixes
- Update package.json with new contributor scripts

Generated-by: GitHub Copilot <copilot@github.com>
Signed-off-by: Ashley Childress <6563688+anchildress1@users.noreply.github.com>

package.json

@@ -8,6 +8,7 @@
     "start": "npm run build",
     "build": "node ./eng/update-readme.mjs",
     "contributors:add": "all-contributors add",
+    "contributors:report": "node ./eng/contributor-report.mjs",
     "contributors:generate": "all-contributors generate",
     "contributors:check": "all-contributors check",
     "collection:validate": "node ./eng/validate-collections.mjs",
@@ -24,7 +25,9 @@
     "copilot",
     "ai",
     "prompts",
-    "instructions"
+    "instructions",
+    "chat modes",
+    "agents"
   ],
   "author": "GitHub",
   "license": "MIT",