Problem: `BaseScraper.submit` was updated to take `file_path` instead of
`source_code`, but cses, codechef, kattis, and usaco still used the old
parameter name, causing basedpyright override errors.
Solution: rename the parameter in all four scrapers. CSES reads the file
content from the path before use. Fix `codechef.fetch_json` missing type
args and `usaco._parse_results_page` narrowing for basedpyright.
## Problem
Codeforces submit was a stub. CSES submit re-ran the full login flow on
every invocation (~1.5s overhead).
## Solution
**Codeforces**: headless browser submit via StealthySession (same
pattern as AtCoder). Solves Cloudflare Turnstile on login, uploads
source via file input, caches cookies at
`~/.cache/cp-nvim/codeforces-cookies.json` so repeat submits skip login.
**CSES**: persist the API token in credentials via a `credentials`
ndjson event. Subsequent submits validate the cached token with a single
GET before falling back to full login.
Also includes a vimdoc table of contents.
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.
