v1.2.2: Add Healthcare specialization, mark cancelled courses, rename Digital Marketing

Apply the J27 (5/6/2026) Stern specialization sheet:

- Add Healthcare (HCR) as the 15th specialization, with HCR cross-listings on
  spr2-health-medical, spr3-analytics-ml, sum2-social-media (renamed), and
  fall1-managing-change. 10 credits available, no required-course gate.
- Rename sum2-social-media to "Digital Marketing Strategy in Practice";
  replace its description with new MSKCC-anchored content; clear instructor
  pending confirmation of new lead.
- Switch from delete-and-replace to the previously-unused cancelled flag
  (Approach B): mark spr5-customer-insights cancelled, add Managing Growing
  Companies back to Summer Set 2 as a cancelled placeholder per the printed
  sheet.
- Update data integrity tests: course count 46 -> 47, spec count 14 -> 15;
  per-spec "across sets" helper now filters cancelled courses so future
  cancellations trigger an obvious assertion failure (BRM 6 -> 5,
  MKT 7 -> 6, HCR 4 new).
- Replace hardcoded 14 in optimizer.test.ts with SPECIALIZATIONS.length.

openspec/changes/j27-spec-update/README.md

@@ -0,0 +1,3 @@
+# j27-spec-update
+
+Apply J27 specialization sheet (5/6/2026): add Healthcare specialization, mark Customer Insights cancelled, add cancelled Managing Growing Companies entry, rename and re-describe Social Media → Digital Marketing Strategy in Practice, add HCR qualifications to four existing courses.