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/components/ResourcesView.tsx

@@ -156,7 +156,7 @@ function FootprintWidget({ usage, onFilter }: FootprintWidgetProps) {
     );
 }
 
-// ── Filter Toggle — Segmented Control ─────────────────────────────────────────
+// ── Filter Toggle - Segmented Control ─────────────────────────────────────────
 
 interface FilterToggleProps {
     value: ResourceFilter;
@@ -429,15 +429,15 @@ export default function ResourcesView() {
     // Derived filtered lists
     const filteredImages = images.filter(img =>
         imageFilter === 'managed' ? img.managedStatus === 'managed' :
-        imageFilter === 'unmanaged' ? img.managedStatus !== 'managed' : true
+            imageFilter === 'unmanaged' ? img.managedStatus !== 'managed' : true
     );
     const filteredVolumes = volumes.filter(vol =>
         volumeFilter === 'managed' ? vol.managedStatus === 'managed' :
-        volumeFilter === 'unmanaged' ? vol.managedStatus !== 'managed' : true
+            volumeFilter === 'unmanaged' ? vol.managedStatus !== 'managed' : true
     );
     const filteredNetworks = networks.filter(net =>
         networkFilter === 'managed' ? net.managedStatus === 'managed' :
-        networkFilter === 'unmanaged' ? net.managedStatus !== 'managed' : true
+            networkFilter === 'unmanaged' ? net.managedStatus !== 'managed' : true
     );
 
     const handleFootprintFilter = (filter: ResourceFilter) => {
@@ -453,7 +453,7 @@ export default function ResourcesView() {
                 <HardDrive className="w-5 h-5 text-muted-foreground" />
                 <h1 className="text-xl font-semibold tracking-tight">Resources Hub</h1>
                 {activeNode?.type === 'remote' && (
-                    <span className="text-sm text-muted-foreground">— {activeNode.name}</span>
+                    <span className="text-sm text-muted-foreground">- {activeNode.name}</span>
                 )}
             </div>
 
@@ -823,7 +823,7 @@ export default function ResourcesView() {
                                     Prune All Docker {confirmPrune?.target}
                                 </AlertDialogTitle>
                                 <AlertDialogDescription>
-                                    This will prune <span className="font-semibold text-foreground">all</span> unused {confirmPrune?.target} from the Docker daemon —
+                                    This will prune <span className="font-semibold text-foreground">all</span> unused {confirmPrune?.target} from the Docker daemon -
                                     including those from <span className="font-semibold text-foreground">external projects not managed by Sencho</span>. This cannot be undone.
                                 </AlertDialogDescription>
                             </>