feat(overlay): add loading OSD spinner and queue notifications until ren

- Show mpv OSD spinner from start-file until subminer-overlay-loading-ready; force-shown for visible-overlay startup regardless of osd_messages setting
- Gate non-macOS overlay visibility on content-ready so first subtitle line is immediately hoverable and clickable
- Queue startup notifications in main process until overlay window finishes loading; upsert progress cards by id to avoid cold-start floods
- Defer background warmups until after overlay runtime init so queued notifications can deliver promptly
- Preserve character dictionary checking/building/importing/ready phases as distinct history entries; route building and importing to system notifications when notificationType is both

plugin/subminer/log.lua

@@ -43,8 +43,8 @@ function M.create(ctx)
 		end
 	end
 
-	local function show_osd(message)
-		if opts.osd_messages then
+	local function show_osd(message, options)
+		if opts.osd_messages or (options and options.force == true) then
 			local payload = "SubMiner: " .. message
 			local sent = false
 			if type(mp.osd_message) == "function" then