Tidy neovim configuration

* Remove some unused plugins and packages.
  * e.g. floaterm, projectionist, vim-wiki, vim-easy-align,
    vim-surround, visual-star-search, vim-rhubarb
* Replace none-ls with conform.nvim and nvim-lint.
* Replace lualine.nvim with mini-statusline.
* Add neodev.
* Simplify cmp completion sources.

justfile

@@ -0,0 +1,8 @@
+_default:
+    just --list
+
+build profile:
+    nix build --json --no-link --print-build-logs ".#{{ profile }}"
+
+check:
+    nix flake check