fix(licensing): rename variant values to skipper/admiral and store resolved type (#379)

Rename internal variant values from 'personal'/'team' to 'skipper'/'admiral',
aligning code with user-facing tier names. Variant type is now resolved once
at activation/validation and stored in DB via license_variant_type, instead
of string-matching the Lemon Squeezy variant_name on every read. Also captures
variant_id for future lookups. Pre-existing installs auto-migrate on first
getVariant() call.

backend/src/services/SchedulerService.ts

@@ -50,7 +50,7 @@ export class SchedulerService {
         try {
             const ls = LicenseService.getInstance();
             const isPaid = ls.getTier() === 'paid';
-            const isAdmiral = isPaid && ls.getVariant() === 'team';
+            const isAdmiral = isPaid && ls.getVariant() === 'admiral';
             if (!isPaid) return; // No scheduled tasks for unpaid tiers
 
             const db = DatabaseService.getInstance();