Persist and restore multiple rulers

[pascalpp]

Implements #234 as part of #228. Adds a schema-versioned UserDefaults ruler-set store, restores saved rulers and active selection on launch, falls back for corrupt data, clears state for UI tests, and migrates old autosaved ruler frames when possible.

[pascalpp]

[codex reviewer] Resetting the active ruler bypasses the state-change notification path that this PR relies on for saving. resetRulerPositions mutates controller.state.settings/layout/visibility directly and calls controller.show() (Free Ruler/AppDelegate.swift:845), while persistence is wired through RulerManager.onStateChanged (Free Ruler/AppDelegate.swift:82) and controller/manager notifyStateChanged (Free Ruler/GroupedRulerWindow.swift:1755). There is no explicit notification/save for reset, so the rulerSetState in UserDefaults can remain stale until applicationWillTerminate happens. A crash or force quit after reset would restore the pre-reset ruler. Please route reset through a controller method that notifies, or explicitly save after resetting, and add a test that prefs.loadRulerSetState() reflects reset immediately after resetRulerPositions.

[pascalpp]

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• Polish multiple ruler integration #244
• Persist and restore multiple rulers #243 👈 (View in Graphite)
• Route ruler commands to active ruler #242
• Split ruler defaults from live settings #241
• Make grouped ruler windows primary #240
• Add multi-ruler manager and lifecycle #239
• Define first-class ruler instance state #238
• feature: Support Multiple Rulers #246 : 9 other dependent PRs (#253 , #255 , #256 and 6 others)
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