fix: add down level ':' keybindings to vim and helix modes

This is for terminals that don't send modifiers at all.

src/keybind/builtin/vim.json

@@ -35,6 +35,7 @@
             ["n", "goto_next_match"],
             ["0", "move_begin"],
             ["<S-4>", "move_end"],
+            [":", "open_command_palette"],
             [";", "open_command_palette"],
             ["<S-;>", "open_command_palette"],
             ["p", "paste"],
@@ -93,6 +94,7 @@
         "syntax": "vim",
         "on_match_failure": "ignore",
         "press": [
+            [":", "open_command_palette"],
             [";", "open_command_palette"],
             ["<S-;>", "open_command_palette"],
             ["b", "open_keybind_config"],