## Problem
Credentials were stored as plaintext JSON in
`stdpath('data')/cp-nvim.json`, with no integration with system
credential managers.
## Solution
Replace file-based credential storage with `git credential
fill/approve/reject`, delegating to whatever credential helper the user
has configured (`cache`, `store`, `libsecret`, macOS Keychain, etc.).
- New `lua/cp/git_credential.lua` module wrapping the git credential
protocol
- All credential consumers (`credentials.lua`, `submit.lua`,
`scraper.lua`) use `git_credential` directly — `cache.lua` no longer
handles credentials
- CSES API token packed into the password field (`password<TAB>token`)
so it works with helpers that ignore the `path` field
- `has_helper()` guard on `:CP login`, `:CP logout`, and `:CP submit`
with an error message if no helper is configured
- Healthcheck split into `[required]`/`[optional]` sections; git version
and credential helper status shown
- `git` checked at startup in `check_required_runtime()`
- Cache version system (`CACHE_VERSION`, v1→v2 migration) removed — the
cache file is now a plain JSON blob
- `:CP` command gets `bar = true`
## Problem
CodeChef had no working login, submit, or contest list. The browser
selectors were wrong, the contest list was missing present/past
contests,
and problem/contest URLs were unset.
## Solution
Fix login and submit selectors for the Drupal-based site. Paginate
`/api/list/contests/past` to collect all 228 Starters, then expand each
parent contest into individual division entries (e.g. `START228 (Div.
4)`).
Add language IDs, correct `url`/`contest_url`/`standings_url` in
metadata,
and make `:CP <platform>` open the contest picker directly.
Problem: vim.loop is deprecated since Neovim 0.10 in favour of vim.uv.
Five call sites across scraper.lua, setup.lua, utils.lua, and health.lua
still referenced the old alias.
Solution: replace every vim.loop reference with vim.uv directly.
