fix: correct Path handling in grep picker

- access dir.filename property instead of dir directly
- convert Path object to string for cwd option

Author: SjB

lua/obsidian/pickers/_snacks.lua

@@ -76,15 +76,15 @@ SnacksPicker.grep = function(self, opts)
     debug_once("grep opts : ", opts)
 
     ---@type obsidian.Path
-    local dir = opts.dir and Path:new(opts.dir) or self.client.dir
+    local dir = opts.dir.filename and Path:new(opts.dir.filename) or self.client.dir
 
     local map = vim.tbl_deep_extend("force", {},
         notes_mappings(opts.selection_mappings))
 
     local pick_opts = vim.tbl_extend("force", map or {}, {
         source = "grep",
         title = opts.prompt_title,
-        cwd = dir,
+        cwd = tostring(dir),
         confirm = function(picker, item, action)
             picker:close()
             if item then