feat: project setup and core models with TDD

MILESTONE 1 COMPLETE:

Project Setup:
- Create .NET 8 MAUI solution targeting iOS, macOS, and web
- Configure nullable reference types and warnings as errors
- Add required dependencies (MAUI 8.0.3, SQLite, CommunityToolkit.Mvvm)
- Add testing dependencies (xUnit, NSubstitute, FluentAssertions, Coverlet)
- Create comprehensive .editorconfig with C# coding standards
- Update CLAUDE.md with development commands

Core Models (TDD - 48 tests, all passing):
- EstimateMode enum (Work, Generic, Humorous modes)
- EstimateResult model with validation (intensity 0.0-1.0, non-null text)
- ShakeData model with intensity validation
- AppSettings model with defaults (Work mode, max history 10)

Build Status:
- All platforms build successfully (net8.0, iOS, macOS)
- 0 warnings, 0 errors
- Test coverage: 51.28% line, 87.5% branch (models have ~100% coverage)

Per spec: Strict TDD followed (RED-GREEN-REFACTOR), models fully validated

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/HihaArvio.Tests/Models/ShakeDataTests.cs

@@ -0,0 +1,106 @@
+using FluentAssertions;
+using HihaArvio.Models;
+
+namespace HihaArvio.Tests.Models;
+
+public class ShakeDataTests
+{
+    [Fact]
+    public void ShakeData_ShouldCreateWithAllProperties()
+    {
+        // Arrange
+        var intensity = 0.65;
+        var duration = TimeSpan.FromSeconds(3);
+        var isShaking = true;
+
+        // Act
+        var shakeData = new ShakeData
+        {
+            Intensity = intensity,
+            Duration = duration,
+            IsShaking = isShaking
+        };
+
+        // Assert
+        shakeData.Intensity.Should().Be(intensity);
+        shakeData.Duration.Should().Be(duration);
+        shakeData.IsShaking.Should().Be(isShaking);
+    }
+
+    [Theory]
+    [InlineData(0.0)]
+    [InlineData(0.25)]
+    [InlineData(0.5)]
+    [InlineData(0.75)]
+    [InlineData(1.0)]
+    public void ShakeData_ShouldAcceptValidIntensityValues(double intensity)
+    {
+        // Act
+        var shakeData = new ShakeData { Intensity = intensity };
+
+        // Assert
+        shakeData.Intensity.Should().Be(intensity);
+    }
+
+    [Theory]
+    [InlineData(-0.1)]
+    [InlineData(-1.0)]
+    [InlineData(1.01)]
+    [InlineData(2.0)]
+    public void ShakeData_ShouldThrowForInvalidIntensity(double invalidIntensity)
+    {
+        // Act
+        Action act = () => _ = new ShakeData { Intensity = invalidIntensity };
+
+        // Assert
+        act.Should().Throw<ArgumentOutOfRangeException>()
+            .WithMessage("*must be between 0.0 and 1.0*");
+    }
+
+    [Fact]
+    public void ShakeData_ShouldAcceptZeroDuration()
+    {
+        // Act
+        var shakeData = new ShakeData { Duration = TimeSpan.Zero };
+
+        // Assert
+        shakeData.Duration.Should().Be(TimeSpan.Zero);
+    }
+
+    [Fact]
+    public void ShakeData_ShouldAcceptPositiveDuration()
+    {
+        // Arrange
+        var duration = TimeSpan.FromSeconds(15.5);
+
+        // Act
+        var shakeData = new ShakeData { Duration = duration };
+
+        // Assert
+        shakeData.Duration.Should().Be(duration);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public void ShakeData_ShouldAcceptBooleanIsShakingValues(bool isShaking)
+    {
+        // Act
+        var shakeData = new ShakeData { IsShaking = isShaking };
+
+        // Assert
+        shakeData.IsShaking.Should().Be(isShaking);
+    }
+
+    [Fact]
+    public void ShakeData_DefaultConstructor_ShouldSetDefaultValues()
+    {
+        // Act
+        var shakeData = new ShakeData();
+
+        // Assert
+        shakeData.Intensity.Should().Be(0.0);
+        shakeData.Duration.Should().Be(TimeSpan.Zero);
+        shakeData.IsShaking.Should().BeFalse();
+    }
+}