TASK 18: local (record-only) recording pipeline + top-bar pills/light/Start-End button UX

Encoder dual-output: StreamEnabled/RecordEnabled/RecordPath options; per-output
ffmpeg block (stream ->flv, record ->mp4); throw unless at least one output.

RecordingFile: auto-name ty-<yyyymmdd>-<start hhmm>-0000.mp4, rename-on-stop to
ty-...-<len hhmmss>.mp4 with numeric-suffix on collision. LayoutStore persists
record folder. MainViewModel: REC/ON-AIR pills, status light, single Start<->End
button (replaces Start/Stop variants), StopStream no longer signs out, explicit
session timer. About overlay widened. Sign In label + spacing before Start.

Tests: 244 passed / 246 (2 pre-existing: AudioPipeline gains-mute, RoundClip).
Build 0 warnings. Scope check clean.

Memory-map correction (derived-solution rule, 2026-08-29): image-shrink recipe was
never recorded when first done, so it was re-derived. Added Derived-solution/recipes
rule to AGENTS.md; MyMistakes.md now a permanent recipes registry (records the
verified WPF-imaging shrink recipe); schema.md rows MyMistakes as registry; ai.md
points to the rule. README hero image replaced: 3.2MB screenshot -> 1400x794 ->
188KB docs/ytLlive-preview.jpg (JPEG q82).

Services/Encoder/FfmpegEncoder.cs

@@ -43,8 +43,12 @@ public sealed class FfmpegEncoder : IFfmpegEncoder
     public async Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default)
     {
         if (options == null) throw new ArgumentNullException(nameof(options));
-        if (string.IsNullOrWhiteSpace(options.RtmpUrl))
-            throw new ArgumentException("An RTMP ingestion URL is required.", nameof(options));
+        var hasStream = options.StreamEnabled && !string.IsNullOrWhiteSpace(options.RtmpUrl);
+        var hasRecord = options.RecordEnabled && !string.IsNullOrWhiteSpace(options.RecordPath);
+        if (!hasStream && !hasRecord)
+            throw new ArgumentException(
+                "At least one output is required — a stream needs an RTMP URL, a recording needs an output path.",
+                nameof(options));
 
         lock (_gate)
         {