Create export-video-list script

Create a `export-video-list` script that exports all the video files on
my external hard drive to a JSON file so I can easily see what videos I
have without needing to get and plug in the drive.

I can easily view it using `bat` or `jq` and combine it with `grep` to
search for a specific video - e.g. `cat ~/video.json | grep -i nix`
(`-i` makes the search case-insensitive).

lib/shared/scripts/export-video-list.nix

@@ -0,0 +1,33 @@
+{ pkgs, ... }:
+{
+  name = "export-video-list";
+
+  runtimeInputs = with pkgs; [
+    jq
+    tree
+    udisks
+  ];
+
+  text = ''
+    device_name="/dev/sda2"
+    device_label="UNTITLED"
+
+    source_path="/run/media/opdavies/$device_label"
+
+    # If the source path doesn't exist, try mounting the device.
+    if [[ ! -d "$source_path" ]]; then
+      ${pkgs.udisks}/bin/udisksctl mount -b "$device_name"
+    fi
+
+    # Exit early if the source path still doesn't exist.
+    if [[ ! -d "$source_path" ]]; then
+      echo "Error: $source_path not found."
+      exit 1
+    fi
+
+    output_file="$HOME/Documents/videos.json"
+
+    ${pkgs.tree}/bin/tree -J "$source_path/Videos" | jq . > "$output_file"
+    ${pkgs.jq}/bin/jq . < "$output_file"
+  '';
+}