add panel.resize CLI verb (T-119)

The keyboard half of panel resizing landed in T-111 (arrow-key
splitters); this completes D-6 user/Claude parity with a CLI verb now
that T-99's IPC dispatch path exists. `clide panel resize <slot> --to N`
sets an absolute pixel size, `--by N` nudges relative to current, and
the reserved `editor` slot drives the editor/bottom-panel split ratio.

The handler lives in panel_commands.dart and stays Flutter-free (so
test/daemon/ keeps running under `dart test`) by talking to an abstract
PanelResizer; the kernel bridge in panel_resizer_kernel.dart wraps
LayoutArrangement and reuses T-111's bumpedSlotSize so the CLI's
relative deltas honour the same right-edge sign-flip as the drag/arrow
handlers. Arguments are lifted from both the direct call shape and the
argv-translator's positional/flags shape pending the typed schema in
T-120. The daemonClientFactory now receives the LayoutArrangement so
the dispatcher can reach it.

Co-Authored-By: Claude <noreply@anthropic.com>

CONTRIBUTING.md

@@ -97,6 +97,9 @@ clide tail --events                  # stream every subsystem event
 clide tail --events --filter git     # stream a single subsystem
 clide pane focus editor              # drive the running app
 clide panel toggle git               # show/hide a panel
+clide panel resize sidebar --to 320  # absolute width (px)
+clide panel resize context --by -40  # relative nudge (px)
+clide panel resize editor --to 0.5   # editor split ratio (0.15–0.70)
 ```
 
 Output is JSON on stdout, one envelope per line. Streaming verbs