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/UsageTests.swift

@@ -79,13 +79,17 @@ struct UsageStatusTests {
     let mondayMorning = date(2025, 1, 6, 10, 0)
 
     private func timeLimitRule(limit: Int = 45) -> BlockingRule {
-        BlockingRule(name: "Time Keeper", kind: .timeLimit, days: Weekday.everyDay,
-                     dailyLimitMinutes: limit)
+        BlockingRule(
+            name: "Time Keeper",
+            configuration: .timeLimit(TimeLimitConfig(dailyLimitMinutes: limit)),
+            days: Weekday.everyDay)
     }
 
     private func openLimitRule(maxOpens: Int = 5) -> BlockingRule {
-        BlockingRule(name: "Gate Keeper", kind: .openLimit, days: Weekday.everyDay,
-                     maxOpens: maxOpens)
+        BlockingRule(
+            name: "Gate Keeper",
+            configuration: .openLimit(OpenLimitConfig(maxOpens: maxOpens)),
+            days: Weekday.everyDay)
     }
 
     @Test("A time-limit rule with budget left is not active")
@@ -153,13 +157,17 @@ struct UsageEnforcementTests {
         let ledger = MockUsageLedger()
         let enforcer = RuleEnforcer(shields: shields, usage: ledger)
         let rule = BlockingRule(
-            name: "Time Keeper", kind: .timeLimit, days: Weekday.everyDay, dailyLimitMinutes: 45)
+            name: "Time Keeper",
+            configuration: .timeLimit(TimeLimitConfig(dailyLimitMinutes: 45)),
+            days: Weekday.everyDay)
         ledger.usageByRule[rule.id] = RuleUsage(minutesUsed: 45)
 
         enforcer.refresh(rules: [rule], at: mondayMorning, calendar: utc)
 
         #expect(shields.shieldedRuleIDs == [rule.id])
         #expect(shields.appliedModes[rule.id] == .block)
+        // Limit rules never engage the adult-content filter (Schedule-only).
+        #expect(shields.appliedAdultContentFlags[rule.id] == false)
     }
 
     @Test("A limit rule with budget left is not shielded")
@@ -168,7 +176,9 @@ struct UsageEnforcementTests {
         let ledger = MockUsageLedger()
         let enforcer = RuleEnforcer(shields: shields, usage: ledger)
         let rule = BlockingRule(
-            name: "Gate Keeper", kind: .openLimit, days: Weekday.everyDay, maxOpens: 5)
+            name: "Gate Keeper",
+            configuration: .openLimit(OpenLimitConfig(maxOpens: 5)),
+            days: Weekday.everyDay)
         ledger.usageByRule[rule.id] = RuleUsage(opensUsed: 2)
 
         enforcer.refresh(rules: [rule], at: mondayMorning, calendar: utc)
@@ -181,9 +191,13 @@ struct UsageEnforcementTests {
 @Suite("Usage display strings")
 struct UsageDisplayTests {
     let timeRule = BlockingRule(
-        name: "Time Keeper", kind: .timeLimit, days: Weekday.everyDay, dailyLimitMinutes: 45)
+        name: "Time Keeper",
+        configuration: .timeLimit(TimeLimitConfig(dailyLimitMinutes: 45)),
+        days: Weekday.everyDay)
     let openRule = BlockingRule(
-        name: "Gate Keeper", kind: .openLimit, days: Weekday.everyDay, maxOpens: 5)
+        name: "Gate Keeper",
+        configuration: .openLimit(OpenLimitConfig(maxOpens: 5)),
+        days: Weekday.everyDay)
 
     @Test("Time-limit rows show minutes used and remaining")
     func timeLimitStrings() {