Add design folder and README

design/shell_window.md

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+# Shell Window Feature
+
+**Purpose**: Interactive pseudo‑terminal session inside a krate.
+
+**Implementation**:
+- Front‑end component uses **xterm.js** (or equivalent) for terminal UI.
+- Backend opens a WebSocket that proxies to `kubectl exec -it <pod> -n <ns> -- sh` (or the container's default shell).
+- Input handling: when the mouse is over the shell window, all keypresses are forwarded to the terminal; space does not trigger Spotlight.
+- Scroll wheel over the terminal scrolls its content; `Ctrl/⌘+scroll` still zooms the canvas.
+- No PTY needed on the server side beyond the exec stream; the WebSocket carries stdin/stdout/stderr.
+
+**Interaction**:
+- Click a result in Spotlight or Collection and press **Alt+S** to open a Shell window in a new/existing Krate.
+- Resize like any Detail Window; sibling windows resize proportionally.
+- Double‑click header or press `z` to maximize to the viewport.
+- The shell window obeys the global pan/zoom shortcuts (Space‑drag pans, Ctrl‑scroll zooms) when the cursor is inside it.
+
+**State** (`Window` type `shell`).