…. Principle III.

Lands the six follow-up migrations the issue tracked plus the
PanLayoutDialog modal special case.  Net: −1102 / +98 lines.

Dialogs migrated:
  PanLayoutDialog          modal fixed-size, no persist key
  MultiFlexDialog          modal, gains FooDialogGeometry
  MidiMappingDialog        non-modal, FramelessWindowTitleBar swap
  MemoryDialog             non-modal, showEvent kept for search focus
  AetherDspDialog          hand-rolled chrome + drag handlers deleted
  NetworkDiagnosticsDialog hand-rolled chrome + 8-axis resize deleted
  DxClusterDialog          tabbed dialog, signal wiring guarded by
                           wasFresh-pattern

Each migration replaces:
  * setFramelessMode() / closeEvent / moveEvent / resizeEvent overrides
  * FramelessResizer::install + manual setFramelessMode(AppSettings…)
    in the ctor
  * Hand-rolled m_titleBar / m_outerLayout / m_bodyLayout members
  * (AetherDsp / NetworkDiag) the entire ~70-line hand-rolled title
    bar widget tree plus FramelessMoveHelper eventFilter cases

…with a single base-class ctor call carrying the title and
"FooDialogGeometry" key.  All six previously-non-persistent dialogs
gain geometry persistence (correction posted to the issue: NONE of
them currently persisted geometry, despite the table claiming four
did — the `geometry()` calls in setFramelessMode were in-process
preservation across frameless toggle, not disk-backed restore).

MainWindow changes:
  * QPointer<QDialog> members re-typed to concrete dialog classes so
    showOrRaisePersistent template binds correctly
  * 6 qobject_cast branches in setFramelessWindow deleted —
    m_persistentDialogs registry now auto-propagates the frameless
    toggle on every PersistentDialog-derived instance
  * NEW ensureAetherDspDialog() helper consolidates 7 duplicated
    AetherDspDialog construct sites — each had been re-pasting the
    same ~17 signal connections wiring NR2/NR4/DFNR/MNR parameter
    changes back to AudioEngine.  Now a single call site.

Verified locally on Linux: open each dialog → resize → close →
restart → reopen — geometry restores per dialog.  Toggle View →
Frameless Window → chrome flips on all of them without losing
geometry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>