Phase 8D: universal deployment package (XP + Win10/11, two entry points)

One RIOJoy-<ver>.zip now deploys on both OS generations (~75 MB with the
offline XP prerequisites):
- Layout: RIOJoy\app (net48 x64) + RIOJoy\app-xp (net40 x86) +
  RIOJoy\vendor (ViGEmBus; vendor\xp: .NET 4.0 offline installer +
  KB2468871, both signature-verified; RioGamepadXP driver slots in when
  8B lands - build warns/skips until then).
- RIOJoy\install-core.bat: shared OS-detecting install logic (ver ->
  5.1 = XP); pure cmd.exe on the XP path, delegates to install-rio.ps1
  on 10/11. Exports RIOJOY_APPDIR for shortcut creation.
- postinstall.bat (TeslaConsole, unattended): elevates, runs the core,
  then deletes install.bat + README.txt so C:\games stays clean.
- install.bat (standalone computers): same core + Start Menu/desktop
  shortcuts via make-shortcut.vbs (XP-safe); keeps the README.
- README.txt at the zip root explains which entry point to run.
- deploy *.ps1 re-encoded UTF-8-with-BOM: Windows PowerShell read the
  BOM-less files as ANSI, where an em-dash byte parses as a curly quote
  and breaks string parsing (bit install-rio.ps1 in dry-run testing).

Verified: zip layout correct; extracted package dispatch-tested on
Win10 non-elevated (OS detect -> modern route -> admin guard, system
untouched).

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

docs/PLAN.md

@@ -294,7 +294,8 @@ Replaces the legacy Google-Sheet → `.data` → GIMP → Script-Fu pipeline
 - To confirm at Phase 7: target wallpaper resolution(s); static wallpaper vs.
   live overlay (e.g. lit-button highlighting mirroring lamp state).
 
-### Phase 8 — Windows XP compatibility (dual-target) — planned
+### Phase 8 — Windows XP compatibility (dual-target) — in progress
+(8A/8C/8D done ✅; remaining: 8B driver + 8E XP-VM/cabinet verification)
 Bring RIOJoy back to the original XP-era cabinets (x86, XP SP3) **without
 regressing Windows 10/11**. Strategy: one codebase, two flavors, **one
 universal deployment archive**. The mapping editor ships everywhere
@@ -310,7 +311,7 @@ XP consumes pre-rendered wallpapers.
 | JSON | System.Text.Json → **Newtonsoft 13** | Newtonsoft 13 (STJ needs net461+; one serializer for both flavors) |
 | Install scripts | PowerShell | **.bat only** (XP has no in-box PowerShell) |
 
-- **8A — Core retarget** (`net48;net40` multi-target): de-Span the
+- **8A — Core retarget — done ✅** (`net48;net40` multi-target): de-Span the
   protocol/serial layer (≈20 uses / 11 files → `byte[]`/`ArraySegment`;
   System.Memory doesn't go below net45, and at 9600 baud Span buys nothing);
   swap System.Text.Json → Newtonsoft in `ConfigStore`/`OverlayTemplateStore`
@@ -341,16 +342,20 @@ XP consumes pre-rendered wallpapers.
   *Staging:* the XP app is useful before the driver lands — milestone 1
   ships keyboard/mouse + lamps + plasma (joystick = Null sink), the driver
   follows as milestone 2.
-- **8C — Tray on net40/x86:** multi-target `RioJoy.Tray` (net40 drops the
+- **8C — Tray on net40/x86 — done ✅:** multi-target `RioJoy.Tray` (net40 drops the
   ViGEm + RioJoy.Overlay references); gate `WallpaperMakerForm` + overlay
   generation; `WallpaperApplier` converts PNG→BMP via GDI+ before
   `SystemParametersInfo` (harmless on 10/11, required on XP); profile editor
   stays (Segoe UI falls back to Tahoma). XP cabinets consume wallpapers
   pre-rendered on a modern machine (`RioProfile.WallpaperPath` travels with
   the config).
-- **8D — Packaging (decided: one universal archive, two install entry
-  points).** `build-package.ps1` produces a single `RIOJoy-<ver>.zip` that
-  deploys on **both** XP and 10/11:
+- **8D — Packaging — done ✅ (one universal archive, two install entry
+  points).** `build-package.ps1` produces a single `RIOJoy-<ver>.zip` (~75 MB
+  with the offline XP redistributables) that deploys on **both** XP and 10/11;
+  the RioGamepadXP driver files bundle automatically once 8B lands
+  (warn/skip until then). The shared OS-detecting install logic lives in
+  `RIOJoy\install-core.bat` (pure cmd on the XP path); shortcuts via
+  `make-shortcut.vbs` (works on XP and 10/11 alike):
   - Layout: `RIOJoy\app\` (net48 x64) + `RIOJoy\app-xp\` (net40 x86) +
     `RIOJoy\vendor\` (ViGEmBus installer for 10/11; RioGamepadXP.sys + INF
     for XP; **.NET 4.0 Full + KB2468871 redistributables** so an offline XP