Replace toggleterm with Snacks.terminal

Snacks.terminal has been driving the terminal keymaps since 6341c73. Carry
<C-\> and <F12> over so the muscle memory survives. The old <M-> binding was
never a valid keycode and could not have fired.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lua/config/keymaps.lua

@@ -14,6 +14,13 @@ vim.keymap.set("n", "<leader>B", function()
   Snacks.terminal({ "btop" }, { esc_esc = false, ctrl_hjkl = false })
 end, { desc = "Toggle btop (improved console top monitor) floating terminal" })
 
+local function toggle_split_terminal()
+  Snacks.terminal.toggle(nil, { win = { position = "bottom" } })
+end
+
+vim.keymap.set({ "n", "t" }, [[<C-\>]], toggle_split_terminal, { desc = "Toggle terminal split" })
+vim.keymap.set({ "n", "t" }, "<F12>", toggle_split_terminal, { desc = "Toggle terminal split" })
+
 -- Toggle zoom/maximize current window (<C-w> is the vim window prefix, m for maximize)
 vim.keymap.set({ "n", "t" }, "<C-w>m", function()
   Snacks.toggle.zoom():toggle()