feat: re-skin to native three-tab UI and add Uninstall Protection

Replace the custom themed presentation with the bare native iOS design
language across a three-tab TabView (Home / Rules / Settings):

- MainTabView hosts the enforcement lifecycle (refresh loop, rule-change
  and scene-active reconcile) so it runs regardless of the selected tab
- HomeView: "Currently Blocking" + "Usage" sections (replaces AppsHomeView)
- RulesListView: rules grouped into Schedule / Time Limit / Open Limit
- SettingsView: Uninstall Protection toggle + Manage App Lists
- AppListLibraryView / ManageAppListsView: shared App List management
- AppSettings: app-group-backed settings store

Uninstall Protection: while enabled and any Hard Mode rule is actively
blocking, deny device app-removal via a dedicated ManagedSettingsStore
(RulePolicy.shouldDenyAppRemoval -> RuleEnforcer -> ShieldController).

Slim AppListPickerSheet to the picker role; drop AppsHomeView and the
custom Theme/HoldToCommitButton/RuleCardView chrome. Update spec section 6
and the unit/UI test suites accordingly.

Shared/ShieldController.swift

@@ -19,6 +19,10 @@ protocol ShieldApplying: AnyObject {
     /// Clears every shield except those for the given rule IDs. Covers rules
     /// that were deleted or expired while the app was not running.
     func clearShields(except activeRuleIDs: Set<UUID>)
+    /// Engages or relinquishes the device-wide app-removal denial used by
+    /// Uninstall Protection. Independent of per-rule shields: it lives on its
+    /// own store so clearing rule shields never disturbs it.
+    func setAppRemovalDenied(_ denied: Bool)
 }
 
 /// Real shield enforcement via per-rule `ManagedSettingsStore`s. Store names
@@ -65,6 +69,17 @@ final class ManagedSettingsShieldController: ShieldApplying {
         }
     }
 
+    func setAppRemovalDenied(_ denied: Bool) {
+        // A dedicated store keeps this device-wide setting off the per-rule
+        // stores, which get fully cleared when their shield lifts. Setting nil
+        // (not false) relinquishes the constraint entirely when off.
+        let store = ManagedSettingsStore(named: Self.uninstallProtectionStoreName)
+        store.application.denyAppRemoval = denied ? true : nil
+    }
+
+    private static let uninstallProtectionStoreName =
+        ManagedSettingsStore.Name("uninstall-protection")
+
     private func store(for ruleID: UUID) -> ManagedSettingsStore {
         ManagedSettingsStore(named: ManagedSettingsStore.Name("rule-\(ruleID.uuidString)"))
     }
@@ -91,6 +106,10 @@ final class MockShieldController: ShieldApplying {
     private(set) var appliedModes: [UUID: SelectionMode] = [:]
     private(set) var appliedAdultContentFlags: [UUID: Bool] = [:]
     private(set) var appliedSelectionData: [UUID: Data?] = [:]
+    /// The device-wide app-removal denial. Deliberately separate from the
+    /// per-rule shield bookkeeping, mirroring the dedicated store in the real
+    /// controller — `clearShields(except:)` must not disturb it.
+    private(set) var appRemovalDenied = false
 
     func applyShield(
         ruleID: UUID, selectionData: Data?, mode: SelectionMode, blockAdultContent: Bool
@@ -115,6 +134,11 @@ final class MockShieldController: ShieldApplying {
             activeRuleIDs.contains($0.key)
         }
         appliedSelectionData = appliedSelectionData.filter { activeRuleIDs.contains($0.key) }
+        // Note: appRemovalDenied is intentionally left untouched here.
+    }
+
+    func setAppRemovalDenied(_ denied: Bool) {
+        appRemovalDenied = denied
     }
 }