Middle-click to kill a process from the panel

I've been using the CPU panel to spot runaway processes, but I still have to switch to htop or the system monitor to actually kill something. Would be useful to do it from the widget directly.

**Proposal:**

- Middle-click a row in the top processes list → confirmation dialog → send SIGTERM to that process
- Shift + middle-click → same thing, no dialog

On hover, something subtle so it's obvious the row is clickable. Cursor change, light highlight, maybe a note in the footer. Left-click stays as-is.

For v1 I'd stick to SIGTERM only. No SIGKILL unless you want it later.

**Implementation-wise this looks straightforward.** `scripts/process-cpu` already returns a `pid` per row; the UI just doesn't use it yet. The panel already runs shell stuff via `Quickshell.Io.Process`, and Omarchy has `ConfirmDialog` for destructive actions. Mostly `Panel.qml` changes.

**Couple things to decide:**

Processes are grouped by name, so when `processCount > 1` you're only killing the representative PID (highest CPU in the sample), not the whole app. We could either warn about that in the dialog or disable kill on grouped rows. What's your preference?

Also worth updating the README security bit since the plugin goes from read-only `/proc` to actually sending signals. Could add an `allowProcessKill` setting if you want it off by default.

Happy to put up a PR if this sounds reasonable.

Start with scripts/process-cpu to confirm the pid and processCount data, then inspect Panel.qml, Quickshell.Io.Process, and Omarchy's ConfirmDialog usage. The work is complete when middle-click and Shift+middle-click behavior, hover feedback, grouped-process handling, and the README security guidance are agreed and covered in the panel.

Written by the indexing model from the issue text.