Add Linux prerequisites and tighten Windows cfg

Update README: rename "Run (Windows dev)" to "Run (dev)", add a Linux (Ubuntu/Debian) prerequisites section with required apt packages and instructions to install Node/Rust and run dev, and clarify the Linux VM build step. Tweak src-tauri/src/main.rs to scope the windows_subsystem attribute to only non-debug Windows builds (add target_os = "windows" to the cfg_attr) to avoid extra console windows in release builds on Windows.

README.md

@@ -31,7 +31,7 @@ Animation and component architecture notes are in [src/styles/shell-guidelines.m
 npm install
 ```
 
-### Run (Windows dev)
+### Run (dev)
 
 ```bash
 npm run dev
@@ -43,6 +43,32 @@ npm run dev
 npm run build
 ```
 
+### Linux prerequisites (Ubuntu/Debian)
+
+Install system dependencies required by Tauri/WebKit:
+
+```bash
+sudo apt update
+sudo apt install -y \
+  libwebkit2gtk-4.1-dev \
+  libappindicator3-dev \
+  librsvg2-dev \
+  patchelf \
+  build-essential \
+  curl \
+  wget \
+  file \
+  libssl-dev \
+  libgtk-3-dev
+```
+
+Install Node.js LTS and Rust (if not already installed), then run:
+
+```bash
+npm install
+npm run dev
+```
+
 ### Controller testing notes (Windows)
 
 - Connect an Xbox-compatible controller before launching dev mode.
@@ -95,8 +121,8 @@ npm install
 
 ### Linux VM build (high-level)
 
-- Install Rust, Node.js, and Tauri Linux prerequisites in the VM.
-- Clone this repo in Linux VM.
+- Install Rust, Node.js, and the Linux prerequisites above.
+- Clone this repo in the Linux VM.
 - Run `npm install`.
 - Run `npm run dev` for integration checks in Linux session.
 - Run `npm run build` to produce Linux artifacts.