feat(atcoder): extract submit helpers; add live status notifications (#294)

## Problem

`_submit_sync` was a 170-line nested closure with `_solve_turnstile` and
the browser-install block further nested inside it. Status events went
to
stderr, which `run_scraper()` silently discards, leaving the user with a
10–30s silent hang after credential entry. The NDJSON spawn path also
lacked stdin support, so submit had no streaming path at all.

## Solution

Extract `_TURNSTILE_JS`, `_solve_turnstile`, `_ensure_browser`, and
`_submit_headless` to module level in `atcoder.py`; status events
(`installing_browser`, `checking_login`, `logging_in`, `submitting`) now
print to stdout as NDJSON. Add stdin pipe support to the NDJSON spawn
path in `scraper.lua` and switch `M.submit` to streaming with an
`on_status` callback. Wire `on_status` in `submit.lua` to fire
`vim.notify` for each phase transition.

scrapers/language_ids.py

@@ -1,7 +1,7 @@
 LANGUAGE_IDS = {
     "atcoder": {
-        "cpp": "5028",
-        "python": "5078",
+        "cpp": "6017",
+        "python": "6082",
     },
     "codeforces": {
         "cpp": "89",