docs: add MODULE_SPEC.md with permission model and capabilities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

MODULE_SPEC.md

@@ -0,0 +1,48 @@
+# rTrips — Trip Planning
+
+**Module ID:** `rtrips`
+**Domain:** `rtrips.online`
+**Version:** 0.1.0
+**Framework:** Next.js 14 / React 18 / Prisma / PostgreSQL
+**Status:** Active
+
+## Purpose
+
+Collaborative trip planning with itineraries, packing lists, shared expenses, and location-based scheduling. Integrates with rMaps for destination visualization and rFunds for expense splitting.
+
+## Data Model
+
+Prisma schema (PostgreSQL). Trips, itineraries, destinations, packing lists, expenses.
+
+## Permission Model
+
+| Capability | Required SpaceRole | Description |
+|-----------|-------------------|-------------|
+| `view_trips` | VIEWER | See trip details and itineraries |
+| `create_trip` | PARTICIPANT | Create new trips |
+| `edit_own_trips` | PARTICIPANT | Modify trips you created |
+| `moderate_trips` | MODERATOR | Edit/manage any trip |
+| `configure_trips` | ADMIN | Space-level trip settings |
+
+**Current Auth:** EncryptID via SDK.
+
+## Canvas Integration
+
+Shape types:
+- **`folk-itinerary`**: Trip timeline with dates and destinations
+- **`folk-packing-list`**: Checklist widget
+- **`folk-destination`**: Location card linked to rMaps
+
+## Cross-Module Dependencies
+
+| Module | Integration |
+|--------|------------|
+| **rMaps** | Destination markers on map |
+| **rFunds** | Expense splitting and budget tracking |
+| **rSpace** | Canvas shape embedding |
+
+## Migration Plan
+
+1. Already has EncryptID auth
+2. Add space-level role resolution
+3. Import `resolveSpaceRole()` + capability checks