fix(finder): handle abort in mini.pick integration

[DefectingCat]

Problem

When mini_pick is enabled as the finder integration, aborting a selection (e.g. pressing <Esc> in the branch picker opened via bb) leaves the find_async coroutine suspended forever. The picker then appears dead — subsequent bb invocations show nothing until Neovim is restarted.

Root cause

Finder:find documents its contract as (finder.lua:307-308):

---Engages finder and invokes `on_select` with the item or items, or nil if aborted

Every integration branch honors this — on_select(nil) is called on abort — except mini_pick:

elseif config.check_integration("mini_pick") then
  local mini_pick = require("mini.pick")
  mini_pick.start { source = { items = self.entries, choose = on_select } }  -- ← no abort path
end

mini.pick's source.choose only fires on explicit confirm (<CR>). Aborting via <Esc> goes through picker_stop, which never calls choose. As a result on_select is never invoked on abort.

Since Finder.find_async = a.wrap(Finder.find, 2), callers using open_async (e.g. checkout_branch_revision via bb) `coroutine.yield` waiting for on_select to resume them. With on_select never firing, the coroutine is permanently suspended.

Compare with how the other integrations handle abort:

Integration	abort → on_select(nil)
vim.ui.select	calls on_select(...) with a nil item
fzf_lua	["esc"] / ["ctrl-c"] / ["ctrl-q"] → close_action → on_select(nil)
telescope	close → on_select(nil)
snacks	on_close → complete(nil) → on_select(nil)
mini_pick	❌ none

Fix

Wire a one-shot MiniPickStop autocmd (mini.pick has no source.on_close field) so an abort still completes the finder via on_select(nil). The new mini_pick_choose helper mirrors the existing snacks_confirm, including the completed guard that ensures on_select runs exactly once.

elseif config.check_integration("mini_pick") then
  local mini_pick = require("mini.pick")
  local choose, on_stop = mini_pick_choose(on_select, self.opts.refocus_status)
  local group = vim.api.nvim_create_augroup("NeogitMiniPickStop", { clear = true })
  vim.api.nvim_create_autocmd("User", {
    pattern = "MiniPickStop", once = true, group = group,
    callback = function()
      vim.api.nvim_clear_autocmds { group = group }
      on_stop()
    end,
  })
  mini_pick.start { source = { items = self.entries, choose = choose } }
end

Reproduce

1. setup({ integrations = { mini_pick = true } })
2. Open neogit status, press bb (branch/revision checkout)
3. Press <Esc> instead of <CR>
4. Press bb again — picker no longer opens; requires restarting Neovim to recover