feat(discovery): add NdiSource record and Teams source string parser

src/TeamsISO.Engine/Discovery/NdiSourceParser.cs

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+using TeamsISO.Engine.Domain;
+
+namespace TeamsISO.Engine.Discovery;
+
+/// <summary>
+/// Parses NDI source strings emitted by Microsoft Teams.
+///
+/// Examples Teams emits:
+///   "MACHINE (Teams - Display Name)"
+///   "MACHINE (Teams)"                — auto-mixed active speaker
+///   "MACHINE (Teams Audio)"          — audio-only mix
+///   "MACHINE (Teams Screen Share)"   — screen share
+/// </summary>
+public static class NdiSourceParser
+{
+    public static NdiSource? Parse(string fullName)
+    {
+        if (string.IsNullOrWhiteSpace(fullName))
+            return null;
+
+        // Find the last '(' so machine names can themselves contain parens.
+        var openParen = fullName.LastIndexOf('(');
+        if (openParen <= 0 || !fullName.EndsWith(')'))
+        {
+            // Try outer parens for cases like "MACHINE (Teams - Smith, Bob (PM))"
+            // by walking from the first '(' that opens a "Teams" inner.
+            var firstParen = fullName.IndexOf(" (Teams", StringComparison.Ordinal);
+            if (firstParen <= 0)
+                return null;
+            openParen = firstParen + 1;
+            if (!fullName.EndsWith(')'))
+                return null;
+        }
+        else
+        {
+            // Re-anchor to the first " (Teams" if present, so display names containing
+            // their own parens (e.g. "Smith, Bob (PM)") don't get truncated.
+            var firstParen = fullName.IndexOf(" (Teams", StringComparison.Ordinal);
+            if (firstParen > 0)
+                openParen = firstParen + 1;
+        }
+
+        var machine = fullName[..openParen].TrimEnd();
+        if (machine.Length == 0)
+            return null;
+
+        var inner = fullName.Substring(openParen + 1, fullName.Length - openParen - 2).Trim();
+
+        if (!inner.StartsWith("Teams", StringComparison.Ordinal))
+            return null;
+
+        if (inner == "Teams")
+            return new NdiSource(fullName, machine, NdiSourceKind.ActiveSpeaker, DisplayName: null);
+        if (inner == "Teams Audio")
+            return new NdiSource(fullName, machine, NdiSourceKind.Audio, DisplayName: null);
+        if (inner == "Teams Screen Share")
+            return new NdiSource(fullName, machine, NdiSourceKind.ScreenShare, DisplayName: null);
+
+        const string prefix = "Teams - ";
+        if (inner.StartsWith(prefix, StringComparison.Ordinal))
+        {
+            var display = inner[prefix.Length..].Trim();
+            if (display.Length == 0)
+                return null;
+            return new NdiSource(fullName, machine, NdiSourceKind.Participant, display);
+        }
+
+        return null;
+    }
+}

src/TeamsISO.Engine/Domain/NdiSource.cs

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+namespace TeamsISO.Engine.Domain;
+
+/// <summary>
+/// Raw discovery record parsed from an NDI source string emitted by Microsoft Teams.
+/// </summary>
+public sealed record NdiSource(
+    string FullName,
+    string MachineName,
+    NdiSourceKind Kind,
+    string? DisplayName);

src/tests/TeamsISO.Engine.Tests/Domain/NdiSourceParserTests.cs

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+using TeamsISO.Engine.Discovery;
+using TeamsISO.Engine.Domain;
+
+namespace TeamsISO.Engine.Tests.Domain;
+
+public class NdiSourceParserTests
+{
+    [Theory]
+    [InlineData("WORKSTATION-01 (Teams - Jane Doe)", "WORKSTATION-01", NdiSourceKind.Participant, "Jane Doe")]
+    [InlineData("PROD-PC (Teams - Élise O'Connor)", "PROD-PC", NdiSourceKind.Participant, "Élise O'Connor")]
+    [InlineData("HOST (Teams - Smith, Bob (PM))", "HOST", NdiSourceKind.Participant, "Smith, Bob (PM)")]
+    public void Parse_Participant_ExtractsMachineAndDisplayName(
+        string fullName, string expectedMachine, NdiSourceKind expectedKind, string expectedDisplay)
+    {
+        var result = NdiSourceParser.Parse(fullName);
+
+        result.Should().NotBeNull();
+        result!.MachineName.Should().Be(expectedMachine);
+        result.Kind.Should().Be(expectedKind);
+        result.DisplayName.Should().Be(expectedDisplay);
+        result.FullName.Should().Be(fullName);
+    }
+
+    [Theory]
+    [InlineData("HOST (Teams)", NdiSourceKind.ActiveSpeaker)]
+    [InlineData("HOST (Teams Audio)", NdiSourceKind.Audio)]
+    [InlineData("HOST (Teams Screen Share)", NdiSourceKind.ScreenShare)]
+    public void Parse_NonParticipantKinds_ClassifyCorrectly(string fullName, NdiSourceKind expectedKind)
+    {
+        var result = NdiSourceParser.Parse(fullName);
+
+        result.Should().NotBeNull();
+        result!.Kind.Should().Be(expectedKind);
+        result.DisplayName.Should().BeNull();
+    }
+
+    [Theory]
+    [InlineData("Plain NDI Source")]
+    [InlineData("HOST (Some Other Software)")]
+    [InlineData("(Teams - No Machine)")]
+    public void Parse_NonTeamsSource_ReturnsNull(string fullName)
+    {
+        var result = NdiSourceParser.Parse(fullName);
+        result.Should().BeNull();
+    }
+}