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/EncoderOptions.cs

@@ -19,6 +19,19 @@ public sealed class EncoderOptions
     public int Fps { get; init; } = 60;
     public int BitrateKbps { get; init; } = 8000;
 
+    /// <summary>Push to <see cref="RtmpUrl"/> (the ON-AIR side). Defaults on so
+    /// the pre-recording callers behave unchanged; the VM sets it from the ON-AIR
+    /// pill.</summary>
+    public bool StreamEnabled { get; init; } = true;
+
+    /// <summary>Write a local file at <see cref="RecordPath"/> (the REC side).
+    /// False unless the REC pill is on.</summary>
+    public bool RecordEnabled { get; init; }
+
+    /// <summary>Local MP4 output path for recording. Required when
+    /// <see cref="RecordEnabled"/> is true.</summary>
+    public string? RecordPath { get; init; }
+
     /// <summary>H.264 encoder name for <c>-c:v</c>; the encoder probes and prefers
     /// nvenc → qsv → amf → libopenh264 when not forced.</summary>
     public string? VideoEncoder { get; init; }