feat: add receipt upload API and target net10

ARCHITECTURE.md

@@ -2,11 +2,11 @@
 
 ## Project Overview
 
-MoneyMap is an ASP.NET Core 8.0 Razor Pages application designed for personal finance tracking. It allows users to import bank transaction CSV files, categorize expenses, attach receipt images/PDFs, and parse receipts using AI (OpenAI GPT-4o-mini Vision API).
+MoneyMap is an ASP.NET Core 10.0 Razor Pages application designed for personal finance tracking. It allows users to import bank transaction CSV files, categorize expenses, attach receipt images/PDFs, and parse receipts using AI (OpenAI GPT-4o-mini Vision API).
 
 ## Technology Stack
 
-- **Framework**: ASP.NET Core 8.0 (Razor Pages)
+- **Framework**: ASP.NET Core 10.0 (Razor Pages)
 - **Database**: SQL Server with Entity Framework Core 9.0
 - **Libraries**:
   - CsvHelper (33.1.0) - CSV parsing
@@ -1214,6 +1214,19 @@ EF Core DbContext managing all database entities.
 
 ## API Endpoints
 
+### Receipt Upload API
+**Route:** `POST /api/receipts?transactionId={id}`
+
+**Purpose:** Upload one receipt image or PDF, store it through `IReceiptManager`, and queue it for asynchronous parsing. Omit `transactionId` to upload an unmapped receipt; provide it to attach the receipt to an existing transaction.
+
+**Request:** `multipart/form-data` with one required `file` field. The shared receipt service accepts JPG/JPEG, PNG, GIF, HEIC, and PDF files up to 10 MB; it validates their file signatures, calculates a SHA-256 hash, and returns duplicate warnings when applicable.
+
+**Responses:**
+- `200 OK`: uploaded receipt metadata (`id`, file metadata, `parseStatus`, optional `transactionId`, and `duplicateWarnings`).
+- `400 Bad Request`: missing/invalid file, unsupported content, over-size upload, duplicate mapped receipt, or unknown transaction.
+
+**Example:** `curl -X POST http://localhost:5010/api/receipts -F 'file=@receipt.png'`
+
 ### Financial Audit API
 **Route:** `GET /api/audit`
 
@@ -1818,7 +1831,7 @@ MoneyMap demonstrates a well-architected ASP.NET Core application with clear sep
 
 **Last Updated:** 2026-02-11
 **Version:** 1.5
-**Framework:** ASP.NET Core 8.0 / EF Core 9.0
+**Framework:** ASP.NET Core 10.0 / EF Core 9.0
 
 ## Recent Changes (v1.5)