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.

flake.nix

@@ -26,10 +26,65 @@
           ps.requests
         ]);
 
+      mkDevPythonEnv =
+        pkgs:
+        pkgs.python312.withPackages (ps: [
+          ps.backoff
+          ps.beautifulsoup4
+          ps.curl-cffi
+          ps.httpx
+          ps.ndjson
+          ps.pydantic
+          ps.requests
+          ps.pytest
+          ps.pytest-mock
+        ]);
+
+      mkSubmitEnv =
+        pkgs:
+        pkgs.buildFHSEnv {
+          name = "cp-nvim-submit";
+          targetPkgs =
+            pkgs: with pkgs; [
+              uv
+              alsa-lib
+              at-spi2-atk
+              cairo
+              cups
+              dbus
+              fontconfig
+              freetype
+              gdk-pixbuf
+              glib
+              gtk3
+              libdrm
+              libxkbcommon
+              mesa
+              libGL
+              nspr
+              nss
+              pango
+              libx11
+              libxcomposite
+              libxdamage
+              libxext
+              libxfixes
+              libxrandr
+              libxcb
+              at-spi2-core
+              expat
+              libgbm
+              systemdLibs
+              zlib
+            ];
+          runScript = "${pkgs.uv}/bin/uv";
+        };
+
       mkPlugin =
         pkgs:
         let
           pythonEnv = mkPythonEnv pkgs;
+          submitEnv = mkSubmitEnv pkgs;
         in
         pkgs.vimUtils.buildVimPlugin {
           pname = "cp-nvim";
@@ -39,12 +94,15 @@
             substituteInPlace lua/cp/utils.lua \
               --replace-fail "local _nix_python = nil" \
               "local _nix_python = '${pythonEnv.interpreter}'"
+            substituteInPlace lua/cp/utils.lua \
+              --replace-fail "local _nix_submit_cmd = nil" \
+              "local _nix_submit_cmd = '${submitEnv}/bin/cp-nvim-submit'"
           '';
           nvimSkipModule = [
             "cp.pickers.telescope"
             "cp.version"
           ];
-          passthru = { inherit pythonEnv; };
+          passthru = { inherit pythonEnv submitEnv; };
           meta.description = "Competitive programming plugin for Neovim";
         };
     in
@@ -58,17 +116,22 @@
       packages = eachSystem (system: {
         default = mkPlugin (pkgsFor system);
         pythonEnv = mkPythonEnv (pkgsFor system);
+        submitEnv = mkSubmitEnv (pkgsFor system);
       });
 
+      formatter = eachSystem (system: (pkgsFor system).nixfmt-tree);
+
       devShells = eachSystem (system: {
         default = (pkgsFor system).mkShell {
           packages = with (pkgsFor system); [
             uv
-            python312
+            (mkDevPythonEnv (pkgsFor system))
             prettier
+            ruff
             stylua
             selene
             lua-language-server
+            ty
           ];
         };
       });