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/stack-management.mdx

@@ -16,7 +16,7 @@ Click **Create Stack** in the left sidebar. Enter a name and click **Create**.
 **Naming rules:**
 - Lowercase letters, numbers, and hyphens only (e.g. `my-app`, `nextcloud`)
 - No spaces or special characters
-- Must be unique — duplicates are rejected
+- Must be unique - duplicates are rejected
 
 Sencho creates a new directory inside `COMPOSE_DIR` with a blank `compose.yaml` file. You'll land in the editor automatically.
 
@@ -34,7 +34,7 @@ Use the **search box** above the list to filter stacks by name.
 
 ## Deploying a stack
 
-Select a stack and click **Deploy** in the stack header. This runs `docker compose up -d` — pulling images if needed and creating or recreating containers.
+Select a stack and click **Deploy** in the stack header. This runs `docker compose up -d` - pulling images if needed and creating or recreating containers.
 
 <Frame>
   <img src="/images/editor/editor-overview.png" alt="Stack editor with control buttons" />
@@ -52,7 +52,7 @@ The stack header exposes four actions:
 | **Delete** | `down` + removes files | Stops and removes containers, then deletes the stack directory. |
 
 <Warning>
-  **Delete** is irreversible. It removes the stack directory — including `compose.yaml`, `.env`, and any bind-mounted files stored there. Back up important files before deleting.
+  **Delete** is irreversible. It removes the stack directory - including `compose.yaml`, `.env`, and any bind-mounted files stored there. Back up important files before deleting.
 </Warning>
 
 ## Stack context menu
@@ -63,8 +63,8 @@ Right-click or use the **⋮** button on any stack in the sidebar to access:
   <img src="/images/stack-management/stack-context-menu.png" alt="Stack context menu showing Alerts option" />
 </Frame>
 
-- **Alerts** — configure metric-based alerting rules for this stack
-- **Check for updates** — manually trigger an image update check
+- **Alerts** - configure metric-based alerting rules for this stack
+- **Check for updates** - manually trigger an image update check
 
 ## Converting a `docker run` command