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/RuleEnforcerTests.swift

@@ -54,7 +54,7 @@ struct RuleEnforcerTests {
     func skipsTimeLimitRules() {
         let shields = MockShieldController()
         let enforcer = RuleEnforcer(shields: shields)
-        let rule = BlockingRule(name: "Time Keeper", kind: .timeLimit)
+        let rule = BlockingRule(name: "Time Keeper", configuration: .timeLimit(TimeLimitConfig()))
 
         enforcer.refresh(rules: [rule], at: mondayDuringWork, calendar: utc)
 
@@ -104,7 +104,8 @@ struct RuleEnforcerTests {
     func forwardsSelectionMode() {
         let shields = MockShieldController()
         let enforcer = RuleEnforcer(shields: shields)
-        let rule = BlockingRule(name: "Focus", selectionMode: .allowOnly)
+        let rule = BlockingRule(
+            name: "Focus", configuration: .schedule(ScheduleConfig(selectionMode: .allowOnly)))
 
         enforcer.refresh(rules: [rule], at: mondayDuringWork, calendar: utc)
 
@@ -115,7 +116,8 @@ struct RuleEnforcerTests {
     func forwardsAdultContentFlag() {
         let shields = MockShieldController()
         let enforcer = RuleEnforcer(shields: shields)
-        let filtered = BlockingRule(name: "Clean Mode", blockAdultContent: true)
+        let filtered = BlockingRule(
+            name: "Clean Mode", configuration: .schedule(ScheduleConfig(blockAdultContent: true)))
         let unfiltered = BlockingRule(name: "Plain")
 
         enforcer.refresh(rules: [filtered, unfiltered], at: mondayDuringWork, calendar: utc)