feat: track limit budgets in a usage ledger and surface them in a Usage section

- RuleUsage + UsageLedger: per-rule, per-day minutes/opens in app-group
  defaults (monotonic minutes, incrementing opens, midnight rollover by
  day-keying); MockUsageLedger for tests and seeded UI scenarios
- usage-aware status: a limit rule whose daily budget is spent on an
  enabled day is active (blocking) until next midnight; Hard Mode gating
  and app-list locking honor it; soft unblock pauses until midnight
- RuleEnforcer shields spent limit rules (always Block mode) while the
  app runs
- new Usage section under Blocked Apps: '18m of 45m used today · 27m
  left', '2 of 5 opens today · 3 opens left', 'Blocked until tomorrow'
- new 'limits' seed scenario + UI tests

OpenAppLock/Views/AppLists/AppListPickerSheet.swift

@@ -15,6 +15,7 @@ struct AppListPickerSheet: View {
 
     @Environment(\.dismiss) private var dismiss
     @Environment(\.modelContext) private var modelContext
+    @Environment(RuleEnforcer.self) private var enforcer
     @Query(sort: \AppList.createdAt) private var lists: [AppList]
     @Query private var rules: [BlockingRule]
 
@@ -22,10 +23,11 @@ struct AppListPickerSheet: View {
     @State private var creatingList = false
     @State private var deletionBlocked = false
 
-    /// While any hard-mode rule is actively blocking, lists are read-only —
-    /// editing one would be a back door out of the hard block.
+    /// While any hard-mode rule is actively blocking (by the clock or a spent
+    /// limit budget), lists are read-only — editing one would be a back door
+    /// out of the hard block.
     private var listsLocked: Bool {
-        !RulePolicy.canEditAppLists(rules: rules)
+        !RulePolicy.canEditAppLists(rules: rules, usageFor: { enforcer.usage(for: $0) })
     }
 
     var body: some View {