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/plugins/toggleterm.lua

@@ -1,44 +0,0 @@
-return {
-  "akinsho/toggleterm.nvim",
-  version = "*",
-  opts = {
-    direction = "horizontal",
-    open_mapping = [[<C-\>]],
-    hide_numbers = true,
-  },
-  cmd = {
-    "ToggleTerm",
-    "TermExec",
-    "ToggleTermSendCurrentLine",
-    "ToggleTermSendVisualLines",
-    "ToggleTermSendVisualSelection",
-    "ToggleTermOpenAll",
-    "ToggleTermCloseAll",
-    "ToggleTermToggleAll",
-  },
-  keys = {
-    [[<C-\>]],
-    { "<M-=>", [[<Cmd>ToggleTerm direction=float<CR>]], desc = "Toggle terminal in floating window" },
-    {
-      "<M->",
-      [[<Cmd>ToggleTerm direction=horizontal<CR>]],
-      desc = "Toggle terminal in horizontal bottom window",
-    },
-    -- tmux muscle-memory for fullscreening nvim window
-    -- replaced with true-zen.nvim
-    -- vim.keymap.set('n', [[<C-a>z]], [[<Cmd>ToggleTermToggleAll<CR>]])
-    -- vim.keymap.set('t', [[<C-a>z]], [[<Cmd>tab split<CR>]])
-    { "<Esc>", [[<C-\><C-n>]], mode = "t", desc = "Escape terminal mode" },
-    { "<Esc><Esc>", [[<Esc>]], mode = "t", desc = "Escape inside terminal" },
-    -- These were replaced by smart-splits
-    -- { "<C-j>", [[<Cmd>wincmd h<CR>]], mode = "t", desc = "Move focus down one window" },
-    -- { "<C-h>", [[<Cmd>wincmd h<CR>]], mode = "t", desc = "Move focus left one window" },
-    -- { "<C-k>", [[<Cmd>wincmd k<CR>]], mode = "t", desc = "Move focus up one window" },
-    -- { "<C-l>", [[<Cmd>wincmd l<CR>]], mode = "t", desc = "Move focus right one window" },
-    { [[<C-\>]], [[<Cmd>ToggleTerm<CR>]] },
-    { "<F12>", [[<Cmd>ToggleTerm<CR>]] },
-    { "<F12>", [[<Cmd>ToggleTerm<CR>]], mode = "t" },
-    -- { "<leader>H", "<cmd>lua _clx_toggle()<CR>", { desc = "Toggle clx (console HackerNews) floating terminal" } },
-    -- { "<leader>G", "<cmd>lua _gitui_toggle()<CR>", { desc = "Toggle gitui floating terminal" } },
-  },
-}