server: fix read_file append_loc space breaking edit_file match (#25705)

server: fix read_file append_loc space breaking edit_file match (#25705)

read_file with append_loc emits "{n}\u2192 {line}". The space after the
arrow is meant as a separator, but it is indistinguishable from real
indentation. Models strip "{n}\u2192" yet keep the space, so the old_text
passed to edit_file carries a phantom leading space and never matches
(normalize_for_fuzzy_match trims trailing whitespace only, never leading).

Drop the separator space so the arrow abuts content: stripping "{n}\u2192"
now yields the exact line with its real indentation preserved, and the
failure mode cannot occur by construction. Update the description example
to match the new format.