Problem: CSES submit was a stub returning "not yet implemented".
Solution: authenticate via web login + API token bridge (POST
`/login` form, then POST `/api/login` and confirm the auth page),
submit source to `/api/courses/problemset/submissions` with
base64-encoded content, and poll for verdict. Uses the same
username/password credential model as AtCoder.
Also update `scraper.lua` to pass the full ndjson event to `on_status`
(instead of just the status string) and handle `credentials` events
for platforms that return updated credentials.
Problem: lua typecheck flagged missing start_time field on ContestSummary;
ty flagged BeautifulSoup Tag/NavigableString union on csrf_input.get(),
a 3-tuple unpack where _extract_problem_info now returns 4 values in
cses.py, and an untyped list assignment in usaco.py.
Solution: add start_time? to ContestSummary LuaDoc, guard csrf_input
with hasattr check and type: ignore, unpack precision from
_extract_problem_info in cses.py callers, and use cast() in usaco.py.
Problem: problem pages contain floating-point precision requirements and
contest start timestamps that were not being extracted or stored. The
submit workflow also needed a foundation in the scraper layer.
Solution: add extract_precision() to base.py and propagate through all
scrapers into cache. Add start_time to ContestSummary and extract it
from AtCoder and Codeforces. Add SubmitResult model, abstract submit()
method, submit CLI case with get_language_id() resolution, stdin/env_extra
support in run_scraper, and a full AtCoder submit implementation; stub
the remaining platforms.
