refactor(nvim): simplify fold config and remove statuscol

Switch to manual folding, remove treesitter foldexpr and statuscol.nvim dependency, simplify snacks statuscolumn config.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

nvim/lua/plugins/snacks.lua

@@ -31,13 +31,7 @@ return {
 
       -- Enhanced statuscolumn
       statuscolumn = {
-        enabled = true,
-        left = { "mark", "sign" },
-        right = { "fold", "git" },
-        folds = {
-          open = true,
-          git_hl = false,
-        },
+        enabled = false,
       },
 
       -- Word highlighting and jumping