Add unit tests, dedupe FFmpeg output filtering, harden settings records

Implements the suggestions from the last review pass:

- Add AmiReel.Tests (MSTest), covering the pure logic in Models/ and
  Services/: SupportedVideoFormats, AppSettings normalization,
  UserFacingErrors.Summarize, the new FfmpegProgressParser/
  FfmpegOutputFilter, RenderPipeline.Validate, BuildProgressMessage, and
  MoveSourceVideos. 59 tests, all passing. UI code-behind and anything that
  spawns an actual FFmpeg process are left to manual/integration testing.
  Exclude AmiReel.Tests\**\*.cs from AmiReel.csproj's default item glob —
  it's a subfolder of the app project now, so without the exclude the app
  itself was compiling the MSTest-only test files.

- Extract the FFmpeg version/library-banner boilerplate list that
  ProcessRunner (live log filter) and UserFacingErrors (error summarizer)
  had each duplicated into a shared FfmpegOutputFilter.IsBoilerplateLine;
  each caller keeps its own remaining context-specific checks on top.
  Also extract ProcessRunner's line-parsing regexes into a standalone
  FfmpegProgressParser so it's directly unit-testable without spawning a
  process.

- Convert AppSettings and RenderSettings from positional record
  constructors to named `required` init properties. Both records had
  runs of same-typed consecutive parameters (three string timing fields
  in AppSettings; three doubles then five ints in RenderSettings) that a
  positional constructor would let get silently transposed at a call site
  without the compiler catching it. Update the two call sites
  (MainPage.xaml.cs) to object-initializer syntax.

- Add Properties/AssemblyInfo.cs with InternalsVisibleTo("AmiReel.Tests")
  and make Validate/BuildProgressMessage/IsNoise internal so tests can
  reach them directly instead of only through process-spawning entry
  points.

- README: document `dotnet test`, and note that Package.appxmanifest's
  Identity is a local-dev placeholder that needs a real publisher/cert
  before MSIX distribution.

Verified: dotnet build (solution + test project) is 0 warnings/errors,
dotnet test is 59/59 passing, and the app still launches unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Services/UserFacingErrors.cs

@@ -39,38 +39,16 @@ public static class UserFacingErrors
         return string.Join(Environment.NewLine, summary);
     }
 
-    private static bool IsNoise(string line)
+    internal static bool IsNoise(string line)
     {
-        return line.StartsWith("ffmpeg version ", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("built with ", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("configuration:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libavutil", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libavcodec", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libavformat", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libavdevice", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libavfilter", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libswscale", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("libswresample", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Input #", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Output #", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Stream mapping:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Stream #", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Metadata:", StringComparison.OrdinalIgnoreCase)
+        return FfmpegOutputFilter.IsBoilerplateLine(line)
             || line.StartsWith("major_brand", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("minor_version", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("compatible_brands", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("encoder", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Duration:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("Press [q] to stop", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("[in#", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("[out#", StringComparison.OrdinalIgnoreCase)
             || line.StartsWith("Last message repeated", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("frame=", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("video:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("audio:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("subtitle:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("other streams:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("global headers:", StringComparison.OrdinalIgnoreCase)
-            || line.StartsWith("muxing overhead:", StringComparison.OrdinalIgnoreCase);
+            || line.StartsWith("frame=", StringComparison.OrdinalIgnoreCase);
     }
 }