Improve startup dictionary sync UX and default playback keybindings

- Add default `f` fullscreen overlay binding and switch default AniSkip skip key to `Tab`
- Make character-dictionary auto-sync non-blocking at startup with tokenization gating for Yomitan mutations
- Add ordered startup OSD progress (checking/generating/updating/importing), refresh current subtitle on sync completion, and extend regression tests

plugin/subminer/options.lua

@@ -1,4 +1,5 @@
 local M = {}
+local DEFAULT_ANISKIP_BUTTON_KEY = "TAB"
 
 local function normalize_socket_path_option(socket_path, default_socket_path)
 	if type(default_socket_path) ~= "string" then
@@ -42,7 +43,7 @@ function M.load(options_lib, default_socket_path)
 		aniskip_payload = "",
 		aniskip_show_button = true,
 		aniskip_button_text = "You can skip by pressing %s",
-		aniskip_button_key = "y-k",
+		aniskip_button_key = DEFAULT_ANISKIP_BUTTON_KEY,
 		aniskip_button_duration = 3,
 	}