terminal: initialize active palette with configured palette

PR #850 introduced several color palette OSC setting and querying
sequencing. In doing so, an active palette was introduced to enable
resetting back to the default (configured) palette. The active palette
was not initialized with the configured palette, thus any configured
theme by the terminal was not set at launch.

This behavior can be confirmed thanks to PR #852, which resets the
active palette on configuration reload. To observe the behavior:

1. Set the configured palette to something other than the default
2. Open ghostty. Observe the color palette
3. Reload the configuration
4. Press enter for a new shell prompt. Note the palette has changed

This patch sets the configured palette as the active palette at
initialization.

src/termio/Exec.zig

@@ -145,6 +145,7 @@ pub fn init(alloc: Allocator, opts: termio.Options) !Exec {
     );
     errdefer term.deinit(alloc);
     term.default_palette = opts.config.palette;
+    term.color_palette.colors = opts.config.palette;
 
     // Set the image size limits
     try term.screen.kitty_images.setLimit(alloc, opts.config.image_storage_limit);