[ALFMOB-421] Add Alfie Companion app, retire DebugMenu, wire config override chain

[amccall-mindera]

ALFMOB-421 — iOS Debug Companion App v1

Implements all agent-doable and Xcode-UI steps. Remaining prerequisite: run ./Alfie/scripts/verify.sh (requires Xcode) and complete TestFlight distribution (step 8) + device end-to-end validation (step 9.2).

What changed

New — shared storage primitives (SPM, no pbxproj)

• AlfieKit/Sources/Model/Services/Persistence/AppGroupUserDefaults.swift — UserDefaultsProtocol wrapper around UserDefaults(suiteName:); falls back to .standard if suite unavailable.
• AlfieKit/Sources/Core/Services/Configuration/Providers/DebugAppConfigurationProvider.swift — reads App Group suite group.com.mindera.alfie.shared at position 0 of the config chain; returns nil when key absent so the chain falls through to Firebase → Local → defaults.

Modified — Alfie/Alfie/Service/ServiceProvider.swift

• sharedDefaults (AppGroupUserDefaults) passed only to ApiEndpointService — companion endpoint override reads from the App Group. userDefaults = .standard kept for BagService/WishlistService to avoid silently relocating persisted data.
• #if DEBUG DebugConfigurationProvider.shared replaced by DebugAppConfigurationProvider() at position 0 unconditionally (no-op when App Group suite is empty).

Removed — DebugMenu SPM module

• Deleted AlfieKit/Sources/DebugMenu/ + DebugConfigurationProvider.swift / DebugConfigurationProviderProtocol.swift.
• Package.swift: removed DebugMenu product, target, Home dep on it, DebugMenuTests target; added Mocks as direct Home dep (was transitive via DebugMenu → Mocks; needed for HomeView #Preview).
• HomeViewModel: removed import DebugMenu, didTapDebugMenu(), fullScreenCover, dead configurationService/apiEndpointService properties.
• HomeDependencyContainer slimmed to sessionService only; AppFeatureViewModel, HomeViewModelProtocol, MockHomeViewModel, Home+Toolbar, ToolbarItemProvider updated accordingly.

New — unit tests

• AlfieKit/Tests/CoreTests/ServiceTests/DebugAppConfigurationProviderTests.swift — override-wins and fall-through paths.
• AlfieKit/Tests/CoreTests/ServiceTests/AppGroupUserDefaultsTests.swift — read/write/remove round-trips.

New — Alfie Companion target + UI (Xcode steps)

• Alfie/Alfie Companion/ — new iOS app target, bundle id com.mindera.alfie.companion, same signing team.
• Alfie/Alfie/Alfie.entitlements — com.apple.security.application-groups added for group.com.mindera.alfie.shared.
• Alfie/Alfie Companion/Alfie Companion.entitlements — same App Group capability on companion side.
• Bundle id collapsed: Debug config now uses com.mindera.alfie (same as Release); Configuration/Debug/GoogleService-Info.plist removed (main app uses single Firebase app).
• Companion UI: CompanionStore.swift (ObservableObject over App Group suite), FlagsView.swift (known + custom flag overrides), EndpointView.swift (endpoint picker + custom URL), InspectorView.swift (Firebase RC + local_config.json + App Group browser + Reset All).
• Alfie_CompanionApp.swift calls FirebaseApp.configure() on launch; ContentView.swift tabs into the three views.
• local_config.json added to companion target via pbxproj build file exception.
• Core and Model SPM package products linked to companion target.

Docs + gitignore

• Removed stale DebugMenu references from Docs/Testing.md, Docs/Architecture.md, Docs/QuickReference.md, README.md.
• Alfie/Alfie Companion/GoogleService-Info.plist added to .gitignore (same pattern as main-app Firebase plists managed by git-secret).

Key invariants for reviewer

1. ServiceProvider.swift: sharedDefaults flows only to ApiEndpointService — BagService/WishlistService at ~lines 98–109 still use self.userDefaults (.standard).
2. ConfigurationKey.allCases used in CompanionStore and FlagsView — this works because ConfigurationKey has an explicit allCases that enumerates only the named cases (excluding .custom(_)), which is exactly the right scope for Reset All and the flags list.
3. endpointKey is private in CompanionStore.swift — not accidentally exported.

Items requiring human verification

• verify.sh — mandatory gate per CLAUDE.md. Must pass before flipping to ready.
• import Firebase in Alfie_CompanionApp.swift — companion links Core (which depends on FirebaseAnalytics, FirebaseCrashlytics, FirebaseRemoteConfig). Verify that the Firebase umbrella module is available at compile time; if not, add FirebaseCore as an explicit package dep in Xcode.
• GoogleService-Info.plist (gitignored) — run git secret reveal or copy the companion plist into Alfie/Alfie Companion/ before building.
• TestFlight distribution (step 8) — create ASC record for com.mindera.alfie.companion, internal eng/QA group; archive and upload.
• Device end-to-end validation (step 9.2) — App Group round-trip requires both apps installed on a real device with release signing.

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