feat: clone Opal's rules feature with hard block enforcement

Rebuild the app around recurring screen-time blocking rules modeled on
Opal's My Apps tab:

- Onboarding with FamilyControls Screen Time authorization
- Apps home with Blocked Apps tiles and live rule cards
- New Rule sheet: Schedule/Time Limit/Open Limit types + preset gallery
- Rule editors: time windows (incl. overnight), day picker, app selection
  via FamilyActivityPicker (Block/Allow Only), rename, Hold to Commit
- Hard Mode: active hard rules cannot be edited, disabled, deleted, or
  unblocked until their window ends; soft rules pause until next window
- Shield enforcement through per-rule ManagedSettingsStore + RuleEnforcer
- 73 unit tests (Swift Testing) + 16 UI tests (XCUITest) with launch-arg
  harness for in-memory storage, mocked authorization, seeded scenarios
- docs/RULES_FEATURE_SPEC.md: spec derived from the reference recording

Known gap: background window transitions and time/open-limit thresholds
need a DeviceActivityMonitor extension; shields currently sync while the
app is running.

Severed/Views/Theme.swift

@@ -0,0 +1,73 @@
+//
+//  Theme.swift
+//  Severed
+//
+
+import SwiftUI
+
+/// Dark, green-tinted palette matching the reference app.
+enum Theme {
+    static let background = Color(red: 0.03, green: 0.05, blue: 0.04)
+    static let surface = Color.white.opacity(0.07)
+    static let surfaceElevated = Color.white.opacity(0.12)
+    static let accent = Color(red: 0.66, green: 0.88, blue: 0.50)
+    static let activeCardTop = Color(red: 0.10, green: 0.20, blue: 0.12)
+    static let activeCardBottom = Color(red: 0.05, green: 0.10, blue: 0.06)
+    static let textSecondary = Color.white.opacity(0.6)
+    static let textTertiary = Color.white.opacity(0.4)
+    static let destructive = Color(red: 1.0, green: 0.32, blue: 0.36)
+
+    static let commitGradient = LinearGradient(
+        colors: [
+            Color(red: 0.35, green: 0.65, blue: 0.85),
+            Color(red: 0.45, green: 0.75, blue: 0.55),
+            Color(red: 0.85, green: 0.80, blue: 0.45),
+        ],
+        startPoint: .leading, endPoint: .trailing
+    )
+}
+
+/// Circular chrome button used in sheet headers (✕, ‹, ✎).
+struct CircleIconButton: View {
+    let systemImage: String
+    var tint: Color = .white
+    let action: () -> Void
+
+    var body: some View {
+        Button(action: action) {
+            Image(systemName: systemImage)
+                .font(.system(size: 15, weight: .semibold))
+                .foregroundStyle(tint)
+                .frame(width: 38, height: 38)
+                .background(Theme.surfaceElevated, in: Circle())
+        }
+        .buttonStyle(.plain)
+    }
+}
+
+/// The "calendar → shield" icon pair shown on rule cards, details, and presets.
+struct RuleIconPair: View {
+    let kind: RuleKind
+    var isActive = false
+
+    var body: some View {
+        HStack(spacing: 8) {
+            iconTile(systemImage: kind.symbolName, tinted: isActive)
+            Image(systemName: "arrow.right")
+                .font(.system(size: 11, weight: .bold))
+                .foregroundStyle(Theme.textTertiary)
+            iconTile(systemImage: "shield.fill", tinted: isActive)
+        }
+    }
+
+    private func iconTile(systemImage: String, tinted: Bool) -> some View {
+        Image(systemName: systemImage)
+            .font(.system(size: 14, weight: .semibold))
+            .foregroundStyle(tinted ? Theme.accent : .white.opacity(0.7))
+            .frame(width: 32, height: 32)
+            .background(
+                (tinted ? Theme.accent.opacity(0.18) : Theme.surfaceElevated),
+                in: RoundedRectangle(cornerRadius: 9)
+            )
+    }
+}