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).

MyMistakes.md

@@ -1,5 +1,46 @@
 # MyMistakes.md
 
-> One task at a time. Updated before every commit touching that task: current iteration +
-> why the last one failed. On task complete, committed AND pushed → truncate to this stub.
-> A new task does NOT seed this file until its first failure.
+> **Two jobs**, distinguished by heading:
+>
+> 1. **Per-task failure log** — updated before every commit touching that task:
+>    current iteration + why the last one failed. On task complete, committed AND
+>    pushed → truncate to this stub. A new task does NOT seed this file until its
+>    first failure.
+> 2. **Recipes registry** (DERIVED-SOLUTION RULE, see `AGENTS.md` 🔬) — the durable
+>    home for one-off derived solutions, recipes, and how-tos. The moment you work
+>    out a reusable solution, write it here **in the same session**. GREP THIS FILE
+>    FIRST when you hit a "I've done this before but have to figure it out again"
+>    wall. Recipe entries stay permanently (they are NOT truncated on task
+>    completion) — only the failure log truncates.
+
+## 🔬 Recipes registry
+
+### Shrink / re-encode an image for the README (screenshots → small hero image)
+
+Worked out 2026-08-29 (the recipe was NEVER recorded the first time it was done, so
+it had to be re-derived from scratch — that's the incident this entry exists to end).
+
+**Approach:** a throwaway Windows-dotnet console app uses WPF's imaging stack
+(`System.Windows.Media.Imaging`) — same framework the app runs on, zero NuGet
+packages, high-quality downscale via `TransformedBitmap`. Screenshots compress
+**far smaller as JPEG than PNG** (PNG 1400px = ~1.2MB; JPEG q82 1400px = ~188KB).
+
+**Recipe (run via the Windows dotnet host from WSL):**
+
+1. Create `imgresize.csproj` targeting `net8.0-windows` with `<UseWPF>true</UseWPF>`
+   (SDK controller). Put it in a Windows-visible temp path, e.g.
+   `C:\Users\gramp\AppData\Local\Temp\imgresize` — NOT `/tmp` (Windows dotnet can't
+   reach a Linux-only path reliably).
+2. `Program.cs`: load `BitmapImage` (`CacheOption=OnLoad` → `Freeze()`), downscale
+   with `TransformedBitmap(src, new ScaleTransform(scale, scale))` to max width
+   (1400 for the README hero), encode with `JpegBitmapEncoder { QualityLevel = 82 }`,
+   save.
+3. Run:
+```bash
+"/mnt/c/Program Files/dotnet/dotnet.exe" run -c Release --project .
+   -- "C:\Users\gramp\Downloads\Screenshot 2026-08-29 075626.png"
+      "C:\Users\gramp\Documents\Code\projects\ytLive\docs\ytLlive-preview.jpg" 1400
+```
+4. Point `README.md` at the `.jpg` (not `.png`).
+
+**Result:** 3.2MB screenshot → 1400×794 → **188KB** `ytLlive-preview.jpg` in `docs/`.