fix(git): use :diffthis to keep diff state out of floating windows

lua/git/diff.lua

@@ -197,26 +197,19 @@ function M.set_buf_name_and_filetype(buf, name)
     end
 end
 
----Apply (or remove) the window-local options that `:diffthis` would
----normally set. Used by both `M.split` here and the sidebar so the two
----diff entry points behave consistently. Vim is supposed to save and
----restore these around the `'diff'` flag flip, but that round-trip is
----fragile when buffers are swapped under an already-diff window.
+---Toggle a window into or out of Vim's diff mode. Goes through the
+---`:diffthis` / `:diffoff` commands rather than `vim.wo[win].diff = X`.
+---The command path runs Vim's full `diff_win_options` setup, which sets
+---an internal flag that prevents subsequently-created floats from
+---inheriting `'diff' = 1` when opened from a focused diff pane. The raw
+---option setter skips that setup, so floats (oil, fzf-lua, etc) end up
+---joining the tabpage's diff group and corrupting its render.
 ---@param win integer
 ---@param enabled boolean
 function M.set_diff(win, enabled)
-    vim.wo[win].diff = enabled
-    if enabled then
-        vim.wo[win].foldmethod = "diff"
-        vim.wo[win].foldenable = true
-        vim.wo[win].foldlevel = 0
-        vim.wo[win].scrollbind = true
-        vim.wo[win].cursorbind = true
-        vim.wo[win].wrap = false
-    else
-        vim.wo[win].scrollbind = false
-        vim.wo[win].cursorbind = false
-    end
+    vim.api.nvim_win_call(win, function()
+        vim.cmd(enabled and "diffthis" or "diffoff")
+    end)
 end
 
 ---@class ow.Git.SplitOpts