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/jj.lua

@@ -1,5 +1,10 @@
 if vim.fn.executable("jj") == 1 then
-    vim.pack.add({ { src = 'https://github.com/NicolasGB/jj.nvim' } })
+    vim.pack.add({ 
+        { src = 'https://github.com/Glhou/jjsigns.nvim', version = 'fix/skip-extra-lines' },
+        { src = 'https://github.com/julienvincent/hunk.nvim' },
+        { src = 'https://github.com/NicolasGB/jj.nvim' },
+        { src = 'https://github.com/rafikdraoui/jj-diffconflicts' },
+    })
     
     local cmd = require("jj.cmd")
     local annotate = require("jj.annotate")