Lock initial DashCaddy billing plan

PRODUCT_PLAN.md

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+# DashCaddy Premium Billing Plan
+
+## Locked Decisions
+
+### Subscription plans
+- 1 month — $25
+- 3 months — $50
+- 6 months — $65
+- 12 months — $99
+
+### Tier model
+DashCaddy has one paid tier: **Premium**.
+All paid plans unlock the same premium features:
+- `sso` — Auto-Login SSO
+- `recipes` — Multi-container stack deployment
+- `swarm` — Docker Swarm multi-node orchestration
+
+### Free tier
+Everything else in DashCaddy remains available without a license.
+No license is required for the free tier.
+
+### Subscription behavior
+- Billing model: recurring Stripe subscriptions
+- Cancellation behavior: access remains active until the paid-through period ends
+- Failed payment behavior: 7-day grace period
+- Renewal behavior: premium access remains active continuously while the subscription is paid
+
+### Licensing behavior
+- License is required only for premium features
+- One active machine per license/subscription at a time
+- License transfer is allowed only after deactivation on the previous machine
+- Existing private lifetime licenses may continue to exist internally, but no public lifetime offering will be sold
+
+### Deployment targets
+- Website source of truth: `dashcaddy.net`
+- Billing/license service repo: `dashcaddy-license-server`
+- Billing/license service deployment target: Contabo
+
+## Architecture Direction
+- Stripe is the billing source of truth
+- DashCaddy license validation remains the product licensing source of truth
+- `dashcaddy-license-server` will bridge Stripe subscriptions to DashCaddy license issuance, renewal, validation, and deactivation
+- Existing DashCaddy license primitives should be reused instead of inventing a second licensing model