[audit] Fix DescribeKey clobbering @a register

[stanfish06]

What

DescribeKey (options.lua:149–151) dumps the output of :map into register @a via redir, then yanks it into a new buffer. Any text previously in @a (e.g. a word yanked with yiw) is silently destroyed.

Where

lua/config/options.lua:150

-- before
vim.cmd("redir @a | silent map | redir END | new | put a")

-- after
local output = vim.fn.execute("map")
vim.cmd("new")
vim.api.nvim_buf_set_lines(0, 0, -1, false, vim.split(output, "\n"))

Why it matters

vim.fn.execute() captures command output as a Lua string without touching any register. The resulting buffer is populated via nvim_buf_set_lines, which is equivalent to the old put a but register-safe. No behavioral change to the user-visible result.

Recommended action

Already applied in this PR. No other changes.

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