Problem: Submit read the source file in Lua, piped the full content as
stdin through to Python, then re-encoded it into an in-memory buffer
just to hand it back to the browser's file input. Unnecessary roundtrip
for AtCoder; CF also gains nothing from Lua owning the read.
Solution: Pass `source_file` path as a CLI arg to the scraper instead
of reading it in Lua and streaming via stdin. AtCoder calls
`page.set_input_files(file_path)` directly. Codeforces reads the file
with `Path(file_path).read_text()` before the browser session. Also
saves the buffer with `vim.cmd.update()` before submitting.
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.
