fix: language version IDs, cache crash, and stress session restore (#352)

## Problem

Codeforces language version IDs were wrong (pointed at old compiler
versions), `LANGUAGE_VERSIONS` was incomplete for most platforms, the
contest picker crashed when `supports_countdown` was stored as a
non-table entry, and `:CP stress` restored a broken IO view on exit.

## Solution

Correct CF `programTypeId` values and default to C++20. Add
`LANGUAGE_VERSIONS` entries for all six platforms. Guard
`get_contest_summaries` against non-table cache entries. Call
`ensure_io_view()` after stress session restore. Shorten the stress
terminal buffer name to a readable `term://stress.py` format.

lua/cp/stress.lua

@@ -53,7 +53,7 @@ local function build_run_cmd(file)
     end
     return './' .. bin
   elseif ext == 'py' then
-    return 'python3 ' .. file
+    return 'python ' .. file
   end
   return './' .. file
 end
@@ -72,6 +72,7 @@ function M.toggle(generator_cmd, brute_cmd)
       state.saved_stress_session = nil
     end
     state.set_active_panel(nil)
+    require('cp.ui.views').ensure_io_view()
     return
   end
 
@@ -128,6 +129,7 @@ function M.toggle(generator_cmd, brute_cmd)
       vim.fn.delete(state.saved_stress_session)
       state.saved_stress_session = nil
     end
+    require('cp.ui.views').ensure_io_view()
   end
 
   execute.compile_problem(false, function(compile_result)
@@ -169,6 +171,11 @@ function M.toggle(generator_cmd, brute_cmd)
 
     vim.cmd.terminal(cmdline)
     local term_buf = vim.api.nvim_get_current_buf()
+    pcall(
+      vim.api.nvim_buf_set_name,
+      term_buf,
+      ("term://stress.py '%s' '%s' '%s'"):format(gen_cmd, brute_run_cmd, binary)
+    )
     local term_win = vim.api.nvim_get_current_win()
 
     local cleaned = false