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/Rules/RuleDetailSheet.swift

@@ -14,6 +14,7 @@ struct RuleDetailSheet: View {
 
     @Environment(\.dismiss) private var dismiss
     @Environment(\.modelContext) private var modelContext
+    @Environment(RuleEnforcer.self) private var enforcer
     @State private var isEditing = false
     @State private var pendingDeletion = false
 
@@ -50,13 +51,14 @@ struct RuleDetailSheet: View {
     }
 
     private func detailList(now: Date) -> some View {
-        let status = rule.status(at: now)
+        let usage = enforcer.usage(for: rule, at: now)
+        let status = rule.status(at: now, usage: usage)
         return List {
             Section {
                 detailRows
             }
             Section {
-                if RulePolicy.canEdit(rule, at: now) {
+                if RulePolicy.canEdit(rule, usage: usage, at: now) {
                     Button {
                         isEditing = true
                     } label: {