feat: RBAC, atomic deployments, fleet backups, and licensing (Pro) (#185)

* feat: add RBAC viewer accounts, atomic deployments, and fleet-wide backups (Pro)

Introduces three Pro-tier features:

- RBAC: Multi-user system with admin/viewer roles, user management UI,
  automatic migration from single-admin credentials, viewer restrictions
  across the entire UI (read-only editor, hidden action buttons)

- Atomic Deployments: Pre-deploy file backup to .sencho-backup/, automatic
  rollback on health probe failure, manual rollback button, health probes
  added to stack updates, webhook-triggered deploys use atomic rollback

- Fleet-Wide Backups: Point-in-time snapshots of compose files across all
  nodes (local + remote), stored centrally in SQLite, per-stack restore
  with optional redeploy, graceful handling of offline nodes

* fix(settings): use correct ProGate prop name in UsersSection

* fix(settings): remove unused isPro prop from UsersSection

* fix(auth): fetch user info after login and setup so isAdmin is set correctly

* feat(pricing): revise pricing strategy and enforce variant-based seat limits

Raise Personal Pro from $49/yr to $69/yr with 3 viewer seats (up from 1).
Add $15/mo billing option for Team Pro. Mark lifetime pricing as a
90-day early-adopter offer. Store Lemon Squeezy variant_name on
activation/validation and enforce seat limits server-side per variant.

* feat(licensing): add Lemon Squeezy checkout, webhook, and billing portal integration

Server-side checkout URL generation (POST /api/checkout) with admin email
pre-fill and instance_id custom data. HMAC-SHA256 verified webhook endpoint
(POST /api/webhooks/lemonsqueezy) handling order, subscription, and payment
lifecycle events for automatic license activation. Customer billing portal
link stored from webhook events and exposed via GET /api/billing/portal.
In-app checkout buttons in Settings with manual license key fallback.

* fix(licensing): exempt Lemon Squeezy webhook from auth middleware

The catch-all auth middleware on /api/* was blocking the public webhook
endpoint. Added /webhooks/lemonsqueezy to the exemption list alongside
/auth/* and /webhooks/:id/trigger.

* feat(pricing): update pricing to final live rates

Personal Pro: $7.99/month, $69.99/year, $249 lifetime.
Team Pro: $49.99/month, $499.99/year, $1,499 lifetime.
Added personal_monthly checkout variant across backend, frontend, and website.

* refactor(licensing): remove server-side checkout/webhook for self-hosted model

Sencho is self-hosted — each user runs their own instance, so there is
no central server to receive webhooks or hold the store API key. Replaced
in-app checkout buttons with a "View Pricing" redirect to sencho.io and
kept manual license key activation as the primary flow.

- Delete LemonSqueezyService (checkout, webhook, HMAC verification)
- Remove POST /api/checkout, GET /api/billing/portal, POST /api/webhooks/lemonsqueezy
- Remove raw body parser and auth exemption for webhook route
- Remove all LEMONSQUEEZY_* env vars from .env.example
- Replace checkout buttons in SettingsModal with single "View Pricing" button
- Simplify LicenseContext checkout to open sencho.io pricing page
- Update licensing docs to reflect website-based purchase flow

* chore: normalize em-dashes to hyphens across codebase (linter)

* chore: remove accidentally tracked directories from index

frontend/src/context/LicenseContext.tsx

@@ -4,15 +4,19 @@ import { apiFetch } from '@/lib/api';
 export type LicenseTier = 'community' | 'pro';
 export type LicenseStatus = 'community' | 'trial' | 'active' | 'expired' | 'disabled';
 
+export type LicenseVariant = 'personal' | 'team' | null;
+
 export interface LicenseInfo {
     tier: LicenseTier;
     status: LicenseStatus;
+    variant: LicenseVariant;
     customerName: string | null;
     productName: string | null;
     maskedKey: string | null;
     validUntil: string | null;
     trialDaysRemaining: number | null;
     instanceId: string;
+    portalUrl: string | null;
 }
 
 interface LicenseContextType {
@@ -22,6 +26,7 @@ interface LicenseContextType {
     refresh: () => Promise<void>;
     activate: (licenseKey: string) => Promise<{ success: boolean; error?: string }>;
     deactivate: () => Promise<{ success: boolean; error?: string }>;
+    checkout: () => void;
 }
 
 const LicenseContext = createContext<LicenseContextType | undefined>(undefined);
@@ -38,7 +43,7 @@ export function LicenseProvider({ children }: { children: ReactNode }) {
                 setLicense(data);
             }
         } catch {
-            // Silently fail — license info is non-critical
+            // Silently fail - license info is non-critical
         } finally {
             setLoading(false);
         }
@@ -83,10 +88,14 @@ export function LicenseProvider({ children }: { children: ReactNode }) {
         }
     }, []);
 
+    const checkout = useCallback(() => {
+        window.open('https://sencho.io/#pricing', '_blank');
+    }, []);
+
     const isPro = license?.tier === 'pro';
 
     return (
-        <LicenseContext.Provider value={{ license, isPro, loading, refresh, activate, deactivate }}>
+        <LicenseContext.Provider value={{ license, isPro, loading, refresh, activate, deactivate, checkout }}>
             {children}
         </LicenseContext.Provider>
     );