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

OpenAppLockUITests/UsageUITests.swift

@@ -0,0 +1,49 @@
+//
+//  UsageUITests.swift
+//  OpenAppLockUITests
+//
+
+import XCTest
+
+/// The Usage section under Blocked Apps — seeded with limit rules at various
+/// budget states ("Time Keeper" 18m/45m, "Gate Keeper" 2/5 opens,
+/// "Doom Scroll" spent → blocked).
+final class UsageUITests: XCTestCase {
+    override func setUpWithError() throws {
+        continueAfterFailure = false
+    }
+
+    func testUsageSectionShowsTimeAndOpenBudgets() throws {
+        let app = XCUIApplication.launchOpenAppLock(seedScenario: "limits")
+
+        XCTAssertTrue(app.staticTexts["Usage"].waitToAppear().exists)
+
+        let timeRow = app.element("usageRow-Time Keeper").waitToAppear()
+        XCTAssertTrue(timeRow.label.contains("18m of 45m used today"), "Got: \(timeRow.label)")
+        XCTAssertTrue(timeRow.label.contains("27m left"), "Got: \(timeRow.label)")
+
+        let openRow = app.element("usageRow-Gate Keeper").waitToAppear()
+        XCTAssertTrue(openRow.label.contains("2 of 5 opens today"), "Got: \(openRow.label)")
+        XCTAssertTrue(openRow.label.contains("3 opens left"), "Got: \(openRow.label)")
+    }
+
+    func testSpentBudgetShowsAsBlockedUntilTomorrow() throws {
+        let app = XCUIApplication.launchOpenAppLock(seedScenario: "limits")
+
+        let spentRow = app.element("usageRow-Doom Scroll").waitToAppear()
+        XCTAssertTrue(spentRow.label.contains("Blocked until tomorrow"), "Got: \(spentRow.label)")
+        // A spent budget is a real block: the rule surfaces in Blocked Apps.
+        XCTAssertTrue(app.buttons["blockedTile-Doom Scroll"].waitToAppear().exists)
+    }
+
+    func testSpentBudgetCanBeUnblockedUntilTomorrow() throws {
+        let app = XCUIApplication.launchOpenAppLock(seedScenario: "limits")
+
+        app.buttons["blockedTile-Doom Scroll"].waitToAppear().tap()
+        app.sheets.buttons["Unblock"].waitToAppear().tap()
+
+        app.staticTexts["nothingBlockedLabel"].waitToAppear()
+        let row = app.element("usageRow-Doom Scroll").waitToAppear()
+        XCTAssertTrue(row.label.contains("Unblocked until tomorrow"), "Got: \(row.label)")
+    }
+}