feat: add line numbers to diff child ops and fix move+edit symbols

Line numbers - Every child op summary now includes the source range as `L{start}–{end}` appended inline (e.g. `added function add L4–8`). Data was already present on SymbolRecord; this threads it through to the display layer.

Move+edit address normalisation - When diffing a renamed+edited file pair, strip the file-path prefix off both trees before calling diff_symbol_trees so that `math_utils.py::add` and `core_math.py::add` normalise to `add` on both sides. Previously every symbol looked deleted-and-added, producing spurious "moved to <name>" entries for functions that were in fact unchanged across the rename.