Document SQLite persistence and local reset behavior

TECH.md

@@ -6,6 +6,7 @@
 - Backend/full-stack project: `RpgRoller` (Minimal API + static `wwwroot` frontend)
 - Frontend source: `RpgRoller/frontend` (TypeScript)
 - Test project: `RpgRoller.Tests` (xUnit + `WebApplicationFactory` integration tests)
+- Persistence: EF Core + SQLite (`RpgRoller/Data/RpgRollerDbContext.cs`)
 - OpenAPI source: `openapi/RpgRoller.json`
 - Generated client source: `RpgRoller/frontend/generated/api-client.ts`
 - Generated client output: `RpgRoller/wwwroot/generated/api-client.js`
@@ -16,11 +17,11 @@
 ## 1) Stack and baseline choices
 
 - ASP.NET Core Minimal API on .NET 10.
-- EF Core + Database in current project (single-node deployment).
+- EF Core with SQLite file persistence in current project (single-node deployment).
 - Cookie authentication (`HttpOnly`, `SameSite=Strict`, secure in production).
 - A minimal frontend framework supporting mixing 3D graphics with 2D elements, or a modern framework-less alternative (HTMl/CSS/TypeScript).
 - OpenAPI generated from backend and consumed by generated client.
-- xUnit integration-heavy test suite with in-memory Database and coverage gates.
+- xUnit integration-heavy test suite with isolated SQLite test databases and coverage gates.
 
 ## 2) Architecture patterns to keep
 
@@ -78,7 +79,7 @@ This pattern is a strong baseline for low to medium scale and should be the defa
 
 ### 2.5 Data and invariants
 
-- Strong DB models
+- Strong DB models backed by SQLite
 - DB-level guardrails (trigger) to complement app-level checks
 - EF patterns:
   - `AsNoTracking()` for read-only queries