refactor: model rule options as a per-kind sum type

Replace the wide BlockingRule/RuleDraft "god struct" — where every option
existed for every kind — with a RuleConfiguration sum type that carries only
the options each kind actually has:

  .schedule(ScheduleConfig: window + selectionMode + blockAdultContent)
  .timeLimit(TimeLimitConfig: dailyLimitMinutes)
  .openLimit(OpenLimitConfig: maxOpens)

Name, days, Hard Mode, app list, and pause stay common to all kinds. This
makes illegal states unrepresentable: Block / Allow Only and Block Adult
Content are now structurally Schedule-only.

User-visible behavior change: the Time Limit and Open Limit editors no longer
offer a Block Adult Content toggle, and their detail sheets drop the "Adult
websites" row — those never made sense for a usage budget. Limit rules are
always Block and never engage the web-content filter.

BlockingRule keeps flat columns as raw persistence behind a computed
`configuration` bridge (lowest SwiftData risk; the cross-process RuleSnapshot
wire format and the Screen Time extensions are untouched). Logic, the editors,
and the detail sheet all switch on the sum type.

Spec (§1, §3.5/§3.6, §5.2) updated first; tests reworked to the new API with
new structural-guarantee unit tests and a UI test asserting the Time Limit
editor/detail omit adult content. Full suite green (180 tests).

Co-Authored-By: Claude <noreply@anthropic.com>

OpenAppLockTests/RuleConfigurationTests.swift

@@ -0,0 +1,44 @@
+//
+//  RuleConfigurationTests.swift
+//  OpenAppLockTests
+//
+
+import Foundation
+import Testing
+
+@testable import OpenAppLock
+
+@MainActor
+@Suite("RuleConfiguration sum type")
+struct RuleConfigurationTests {
+    @Test("Each case reports its kind")
+    func kindDerivation() {
+        #expect(RuleConfiguration.schedule(ScheduleConfig()).kind == .schedule)
+        #expect(RuleConfiguration.timeLimit(TimeLimitConfig()).kind == .timeLimit)
+        #expect(RuleConfiguration.openLimit(OpenLimitConfig()).kind == .openLimit)
+    }
+
+    @Test("Defaults match the reference app's new-rule defaults")
+    func defaults() {
+        let schedule = RuleConfiguration.default(for: .schedule).scheduleConfig
+        #expect(schedule?.startMinutes == 9 * 60)
+        #expect(schedule?.endMinutes == 17 * 60)
+        #expect(schedule?.selectionMode == .block)
+        #expect(schedule?.blockAdultContent == false)
+
+        #expect(RuleConfiguration.default(for: .timeLimit).timeLimitConfig?.dailyLimitMinutes == 45)
+        #expect(RuleConfiguration.default(for: .openLimit).openLimitConfig?.maxOpens == 5)
+    }
+
+    @Test("Typed projections only unwrap the matching case")
+    func projections() {
+        let schedule = RuleConfiguration.schedule(ScheduleConfig(blockAdultContent: true))
+        #expect(schedule.scheduleConfig?.blockAdultContent == true)
+        #expect(schedule.timeLimitConfig == nil)
+        #expect(schedule.openLimitConfig == nil)
+
+        let openLimit = RuleConfiguration.openLimit(OpenLimitConfig(maxOpens: 7))
+        #expect(openLimit.openLimitConfig?.maxOpens == 7)
+        #expect(openLimit.scheduleConfig == nil)
+    }
+}