The agent_pane_min_width config value was accepted in the schema and
passed as CapacityConfig.agentPaneWidth but never actually used — the
underscore-prefixed _config parameter in decideSpawnActions was unused,
and all split/capacity calculations used the hardcoded MIN_PANE_WIDTH.
Now decideSpawnActions, canSplitPane, isSplittableAtCount,
findMinimalEvictions, and calculateCapacity all accept and use the
configured minimum pane width, falling back to the default (52) when
not provided.
Closes#1781
YeonGyu-Kim
e8abf6d696