add-plan-based-featureslisted

# Plan-Based Features ## Overview This template uses a **3-layer feature system** stored in JSONB. Features are managed via Manager app and validated via `IPlanService`. **DO NOT create new guards, schemas, or feature systems - use the existing pattern.** ## When to Use - Adding a new boolean feature (flag) gated by plan - Adding a new numeric limit (workspaces, users, projects) - Validating feature access in a controller/service - Modifying which plans have access to a feature ## When NOT to Use - Non-plan-gated authentication or session checks - Role-based access control (RBAC) unrelated to subscription tier - Generic feature flags (A/B tests, experiments) unrelated to billing - Per-user preferences or workspace settings stored outside plans ## The 3-Layer Structure | Layer | Purpose | Example | |-------|---------|---------| | `limits` | Numeric caps | `workspaces:3, usersPerWorkspace:5` | | `flags` | Boolean toggles | `reportsExport:true, apiAccess:false` | | `display` | UI display | `badge, ctaText, displayFeatures[]` | ```typescript // libs/domain/src/types/PlanFeatures.ts interface PlanFeatures { limits: PlanLimits; // Quantitative constraints flags: PlanFlags; // Boolean toggles display: PlanDisplay; // UI/marketing info } ``` ## Key Files (DO NOT RECREATE) | File | Purpose | |------|---------| | `libs/domain/src/types/PlanFeatures.ts` | Type definitions | | `libs/backend/src/billing/IPlanService.ts` | Validation interface | | `apps/backend/src/a