Adds a getOwnerSettings read query to scheduler_core (previously only
an internal helper existed) and an updateOwnerSettings command on the
Flutter command controller, then builds a shared Settings dialog
surfacing timezone, day window, compact mode, and backlog staleness
thresholds. Both existing no-op entry points (sidebar nav item, top
bar button) now open the same dialog and persist edits through the
existing OwnerSettings/BacklogStalenessSettings backend.
Per the design spec (circuitforge-plans/focus-flow/superpowers/specs/
2026-07-07-settings-screen-design.md), the compact-mode toggle
persists but is disclosed in-UI as not yet affecting Today rendering,
since that wiring is separate scope (#11).
Closes: #16
