refactor(config/nvim): move pack.add declarations into individual plugin files

The monolithic vim.pack.add() table in init.lua was removed and each
plugin/*.lua file now declares its own dependencies via vim.pack.add()
at the top. tools.lua was decomposed into per-plugin files (cmake.lua,
jupynvim.lua, just.lua, kulala.lua, mise.lua, neogit.lua, sshfs.lua,
trouble.lua, undotree.lua, zoxide.lua) each with their own config and
keymaps. This makes plugin files self-contained and easier to maintain.

config/nvim/plugin/mise.lua

@@ -0,0 +1,13 @@
+if vim.fn.executable("mise") == 1 then
+    vim.pack.add({
+        { src = 'https://plugins.ejri.dev/mise.nvim' },
+    })
+
+    require('mise').setup({
+        unset_vars = true,
+        load_on_setup = true,
+        force_run = true,
+    })
+
+    vim.keymap.set({'n'}, '<leader>xM', '<cmd>Lazy reload mise.nvim<cr>', { desc = "Reload mise environment"  })
+end