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

docs/features/app-store.mdx

@@ -3,7 +3,7 @@ title: App Store
 description: Browse and deploy pre-configured application templates in one click.
 ---
 
-The **App Store** tab lets you browse a curated catalogue of Docker Compose templates and deploy any of them as a new stack with environment-specific configuration — no YAML required.
+The **App Store** tab lets you browse a curated catalogue of Docker Compose templates and deploy any of them as a new stack with environment-specific configuration - no YAML required.
 
 <Frame>
   <img src="/images/app-store/app-store-overview.png" alt="App Store showing a grid of application templates with category filters" />
@@ -30,7 +30,7 @@ Click any template card to open the **deployment sheet** on the right side of th
 
 ### Stack name
 
-Pre-filled with the template name in lowercase. You can change it — the same [naming rules](/features/stack-management#creating-a-stack) apply (lowercase, hyphens, no spaces).
+Pre-filled with the template name in lowercase. You can change it - the same [naming rules](/features/stack-management#creating-a-stack) apply (lowercase, hyphens, no spaces).
 
 ### Environment variables
 
@@ -48,7 +48,7 @@ For each container mount point, enter the **host path** where that data should b
 
 ### Ports
 
-For each exposed port, edit the **host port** (left side). The container port (right side) is fixed by the template and cannot be changed here — edit the compose file after deployment if needed.
+For each exposed port, edit the **host port** (left side). The container port (right side) is fixed by the template and cannot be changed here - edit the compose file after deployment if needed.
 
 ### What happens on Deploy