feat: GPU process list with per-process VRAM/utilization and kill

Add a GPU process table to the Performance tab showing which processes
use the selected GPU, with per-process VRAM, GPU utilization, CPU, host
memory, and command. Includes a kill endpoint (SIGTERM/SIGKILL, with
optional parent kill) behind a confirm dialog.

- nvcurve/hal/processes.py: NVML + /proc process enumeration
- server.py: GET /api/processes, POST /api/processes/kill (refuses to
  signal init/kthreadd)
- frontend: ProcessList component, API client, types
- tests: test_processes.py
- docs: API reference for the new endpoints

frontend/src/components/common/ConfirmDialog.tsx

@@ -1,10 +1,20 @@
+export interface DialogAction {
+  label: string;
+  onClick: () => void;
+  className?: string;
+  disabled?: boolean;
+}
+
 interface Props {
   message: string;
   detail?: string;
   confirmLabel?: string;
   isDestructive?: boolean;
-  onConfirm: () => void;
+  /** Required unless `actions` is provided (which replaces the single confirm button). */
+  onConfirm?: () => void;
   onCancel: () => void;
+  /** When provided, rendered after Cancel instead of the single confirm button. */
+  actions?: DialogAction[];
 }
 
 export function ConfirmDialog({
@@ -14,6 +24,7 @@ export function ConfirmDialog({
   isDestructive = false,
   onConfirm,
   onCancel,
+  actions,
 }: Props) {
   return (
     <div
@@ -33,17 +44,34 @@ export function ConfirmDialog({
           >
             Cancel
           </button>
-          <button
-            onClick={onConfirm}
-            className={[
-              "px-3 py-1.5 rounded text-xs font-semibold transition-colors",
-              isDestructive
-                ? "bg-red-600 hover:bg-red-500 text-white"
-                : "bg-emerald-600 hover:bg-emerald-500 text-white",
-            ].join(" ")}
-          >
-            {confirmLabel}
-          </button>
+          {actions ? (
+            actions.map((a) => (
+              <button
+                key={a.label}
+                onClick={a.onClick}
+                disabled={a.disabled}
+                className={[
+                  a.className ??
+                    "px-3 py-1.5 rounded bg-zinc-800 hover:bg-zinc-700 text-zinc-200 text-xs font-semibold transition-colors",
+                  a.disabled ? "opacity-40 cursor-not-allowed" : "",
+                ].join(" ")}
+              >
+                {a.label}
+              </button>
+            ))
+          ) : (
+            <button
+              onClick={() => onConfirm?.()}
+              className={[
+                "px-3 py-1.5 rounded text-xs font-semibold transition-colors",
+                isDestructive
+                  ? "bg-red-600 hover:bg-red-500 text-white"
+                  : "bg-emerald-600 hover:bg-emerald-500 text-white",
+              ].join(" ")}
+            >
+              {confirmLabel}
+            </button>
+          )}
         </div>
       </div>
     </div>