fix: let CLI options take precedence over user settings

[meox]

Problem

Options set in ~/.config/pix/settings.exs silently override values passed explicitly on the command line.

Each command handler merges the user settings on top of the parsed CLI options:

cli_opts = Keyword.merge(cli_opts, user_settings.command.shell.cli_opts)

Keyword.merge(a, b) gives precedence to the second argument, so the settings file wins over the CLI.

Reproduction

With a settings default:

%{command: %{shell: %{cli_opts: [ssh: "default=~/.ssh/id_ed25519_work"]}}}

running:

pix shell --ssh="default=~/.ssh/vm_key" dev_tools remote_load.sh my_service:latest 192.168.64.9

still mounts id_ed25519_work and discards the explicit --ssh value:

>>> mounting SSH key "/home/meox/.ssh/id_ed25519_work" as /root/.ssh/id_ed25519_work into shell container
root@192.168.64.9: Permission denied (publickey).

Fix

Swap the Keyword.merge argument order so user settings act as defaults and explicit CLI options take precedence:

cli_opts = Keyword.merge(user_settings.command.shell.cli_opts, cli_opts)

Applied consistently across all command handlers that perform this merge: shell, run, ls, graph, upgrade.

Notes

• Options not provided on the CLI still fall back to the settings value, so existing settings.exs defaults keep working.
• For multi-value (:keep) options such as ssh/secret/arg, an explicit CLI value now replaces the settings default for that key (CLI wins) rather than being clobbered by it.

Verification

• mix compile --warnings-as-errors passes (pix app)
• mix format --check-formatted passes