fix(licensing): resolve Admiral variant detection and lifetime license handling (#376)

* fix(licensing): resolve Admiral variant detection and lifetime license handling

The Lemon Squeezy variant name for Admiral licenses contains "Admiral"
(not "Team"), but getVariant() only checked for "team" and "personal".
This caused Admiral licenses to be misidentified as Skipper, locking all
Admiral-exclusive features.

- Map "admiral" variant names to internal "team" value, "skipper" to "personal"
- Add isLifetime field to LicenseInfo API response
- Hide "Manage Subscription" button for lifetime licenses (no billing portal)
- Show "Duration: Lifetime" instead of empty renewal date
- Hide upgrade cards for active Admiral users
- Add 23 unit tests covering variant resolution, tier computation, and lifetime detection
- Add troubleshooting entries for wrong tier label, locked features, and billing portal errors

* fix(licensing): address code review findings

- Fix nested ternary in LicenseSection JSX; restore conditional rendering
  to avoid showing an empty "N/A" row for non-subscription states
- Clean up test file: use shared svc variable, remove redundant comments,
  add trialDaysRemaining assertions, rename describe block

frontend/src/context/LicenseContext.tsx

@@ -17,6 +17,7 @@ export interface LicenseInfo {
     trialDaysRemaining: number | null;
     instanceId: string;
     portalUrl: string | null;
+    isLifetime: boolean;
 }
 
 interface LicenseContextType {