extras: add PowerShell greeting port, Rust gm-switch and Windows installers

- powershell_greeting: PowerShell port of fish_greeting (fastfetch random logo, sixel/kitty-direct per terminal, logs, modes)

- win-gm-switch: Rust port of gm-switch.cpp (cross-platform mode file, --status, Start Menu shortcuts installer)

- install-windows.ps1 umbrella installer; README pointers

README.md

@@ -8,7 +8,7 @@ Self-hosted media library and e621 archive manager, rebuilt as a **React SPA + D
 backend/    Django 6 + DRF API (MariaDB + Redis via docker compose)
 frontend/   Vite + React + TypeScript SPA
 deploy/     Docker images, compose variants and Tailscale serve configs
-extras/     shell integrations (fish_greeting with fastfetch)
+extras/     shell integrations (fish + PowerShell greetings with fastfetch, gm-switch)
 ```
 
 ## Development
@@ -75,8 +75,11 @@ curl -H "Authorization: Token <token>" \
   the bundled nginx those aliases negotiate on `Accept`: browsers get the SPA
   page, requesters like curl/wget/fastfetch get the JSON. `/api/random/` is
   the unambiguous path for scripts; 404 when nothing matches the filters.
-- A ready-made shell greeting that uses this endpoint lives in
-  [`extras/fish_greeting/`](extras/fish_greeting/README.md).
+- Ready-made shell greetings that use this endpoint live in
+  [`extras/fish_greeting/`](extras/fish_greeting/README.md) (Linux/fish) and
+  [`extras/powershell_greeting/`](extras/powershell_greeting/README.md)
+  (Windows/PowerShell); [`extras/win-gm-switch/`](extras/win-gm-switch/)
+  (Rust) switches the rating mode on both.
 - **Scoped tokens for scripts**: the Account page's *Shell tokens* section
   (also `/tokens`) issues `j621r_…` tokens that only authenticate
   `/api/random/` — the rest of the API rejects them. They are stored as