Add Project Structure

Project-Structure.md

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+# Project Structure
+
+```
+.
+├── main.go                          # Entry point — HTTP routes, CORS middleware, shell loop
+├── app.db                           # SQLite database (auto-created on first run)
+├── build.sh                         # Build script → outputs ./Portifolio binary
+├── go.mod / go.sum
+└── internal/
+    ├── database/
+    │   └── main.go                  # InitDB (all CREATE TABLE statements)
+    │                                # GetTrades, UpdatePositions, and other DB helpers
+    ├── handlers/
+    │   ├── main.go                  # HealthHandler
+    │   ├── company.go               # AddCompanyHandler, GetCompaniesHandler,
+    │   │                            # GetCompanyRevenueCategories
+    │   ├── currency.go              # AddCurrencyHandler, GetCurrenciesHandler
+    │   ├── revenue.go               # AddRevenueEntryHandler
+    │   └── trade.go                 # AddTradeHandler, GetTradeListHandler,
+    │                                # GetPositionListHandler
+    ├── model/
+    │   ├── company.go               # Company struct
+    │   ├── currency.go              # Currency struct
+    │   ├── periode.go               # Period struct + QuarterPeriod, HalfYearPeriod,
+    │   │                            # FullYearPeriod helpers
+    │   ├── portifolio.go            # Position, Trade, TradeProduct, TradeType,
+    │   │                            # AddTradeRequest (with Validate()), Portfolio
+    │   └── revenue.go               # Revenue, RevenueReport, RevSum structs
+    ├── service/
+    │   ├── currency.go              # Currency business logic
+    │   └── portfolio.go             # UpdatePositionByTradeList — rebuilds positions
+    │                                # from full trade history
+    └── shell/
+        ├── company.go               # add-company, list-companies
+        ├── currency.go              # add-currency, list-currency
+        └── revenue.go               # add-revenue, list-revenue
+```
+
+## Key Design Points
+
+**`main.go`** wires together the HTTP mux and the shell loop. Both run concurrently — the HTTP server is started in a goroutine and the shell blocks on stdin.
+
+**`internal/database`** owns all SQL. Handlers and services call functions here rather than writing raw queries themselves.
+
+**`internal/model`** contains only structs, enums, and validation. No SQL lives here.
+
+**`internal/service`** contains business logic that spans multiple database calls. `UpdatePositionByTradeList` replays the full trade history to compute current positions, then writes them back to the database.
+
+**`internal/handlers`** are thin — they decode the request, call a service or database function, and encode the response.