feat(insurance): resolve coverage percent per service category

Base insurance is a percentage-only rule: patient share is now total minus the
base share, and the contract franchise no longer inflates it (franchise stays
meaningful for supplementary contracts only).

Coverage percentages are managed centrally by admin per service category
(outpatient/inpatient, extensible via the ServiceCategory enum). A tenant
contract may override a category, otherwise it follows the admin default live —
changing the central value immediately applies to every contract that did not
override it.

- add ServiceCategory enum + GET /api/v1/service-categories as the single source
  of the category list for every client
- add insurance_coverage_defaults (+ GET/PUT admin coverage-defaults endpoints)
  and expose coverage_defaults on the insurance list and insurance-pricing
- add tenant_insurance_category_coverage; tenant-insurances accepts optional
  category_coverages (needs insurances.update) and returns the effective
  percentages with their source
- add service_items.service_category; visits always resolve as outpatient
- drop the reverse-engineered percent from patient_share_rials in MyPatientsPage
  and align the client-side BillingCalculator mirror in CreateStep

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

phpstan-baseline.neon

@@ -87,7 +87,7 @@ parameters:
 		-
 			message: '#^Using nullsafe property access "\?\-\>franchiseRials" on left side of \?\? is unnecessary\. Use \-\> instead\.$#'
 			identifier: nullsafe.neverNull
-			count: 2
+			count: 1
 			path: src/Billing/Service/BillingCalculator.php
 
 		-