Add monetization app with RevenueCat webhooks alongside Stripe.

Rename finance → monetization (keep finance_* tables via app label), add
RevenueCat webhook + ledger upserts so store IAP syncs subscriptions and
billing history like Stripe. Companion to chat_web_app#100 / #68.

llm_be/monetization/admin.py

@@ -0,0 +1,133 @@
+from django.contrib import admin
+
+from monetization.models import BackerEmail, Invoice, Payment, SubscriptionPlan, UserSubscription
+
+
+@admin.register(SubscriptionPlan)
+class SubscriptionPlanAdmin(admin.ModelAdmin):
+    list_display = (
+        "slug",
+        "name",
+        "price_cents",
+        "is_public",
+        "is_selectable",
+        "allows_image_generation",
+        "allows_rag",
+        "allows_all_future_features",
+        "prompt_quota_per_window",
+        "prompt_window_hours",
+        "monthly_token_quota",
+        "sort_order",
+    )
+    list_filter = ("is_public", "is_selectable", "allows_image_generation", "allows_rag")
+    search_fields = ("slug", "name", "stripe_price_id")
+    readonly_fields = ("created", "last_modified")
+    prepopulated_fields = {"slug": ("name",)}
+
+
+@admin.register(BackerEmail)
+class BackerEmailAdmin(admin.ModelAdmin):
+    list_display = ("email", "note", "redeemed_at", "redeemed_user", "created")
+    search_fields = ("email", "note", "redeemed_user__email")
+    raw_id_fields = ("redeemed_user",)
+    readonly_fields = ("created", "last_modified", "redeemed_at", "redeemed_user")
+
+
+@admin.register(UserSubscription)
+class UserSubscriptionAdmin(admin.ModelAdmin):
+    list_display = (
+        "user",
+        "plan",
+        "status",
+        "source",
+        "stripe_subscription_id",
+        "monthly_token_quota_override",
+        "created",
+    )
+    list_filter = ("status", "source", "plan")
+    search_fields = ("user__email", "user__username", "stripe_subscription_id")
+    raw_id_fields = ("user", "plan")
+    readonly_fields = ("created", "last_modified")
+
+
+class PaymentInline(admin.TabularInline):
+    model = Payment
+    extra = 0
+    readonly_fields = (
+        "provider",
+        "status",
+        "amount",
+        "currency",
+        "stripe_payment_intent_id",
+        "stripe_charge_id",
+        "paid_at",
+        "failure_message",
+        "created",
+        "last_modified",
+    )
+    can_delete = False
+    show_change_link = True
+
+
+@admin.register(Invoice)
+class InvoiceAdmin(admin.ModelAdmin):
+    list_display = (
+        "id",
+        "user",
+        "company",
+        "provider",
+        "status",
+        "amount_due",
+        "amount_paid",
+        "currency",
+        "period_start",
+        "period_end",
+        "stripe_invoice_id",
+        "stripe_checkout_session_id",
+        "created",
+    )
+    list_filter = ("provider", "status", "currency")
+    search_fields = (
+        "user__email",
+        "user__username",
+        "company__name",
+        "stripe_invoice_id",
+        "stripe_checkout_session_id",
+        "stripe_subscription_id",
+        "stripe_customer_id",
+        "description",
+    )
+    readonly_fields = ("created", "last_modified")
+    raw_id_fields = ("user", "company")
+    inlines = [PaymentInline]
+    date_hierarchy = "created"
+
+
+@admin.register(Payment)
+class PaymentAdmin(admin.ModelAdmin):
+    list_display = (
+        "id",
+        "user",
+        "company",
+        "invoice",
+        "provider",
+        "status",
+        "amount",
+        "currency",
+        "stripe_payment_intent_id",
+        "stripe_charge_id",
+        "paid_at",
+        "created",
+    )
+    list_filter = ("provider", "status", "currency")
+    search_fields = (
+        "user__email",
+        "user__username",
+        "company__name",
+        "stripe_payment_intent_id",
+        "stripe_charge_id",
+        "invoice__stripe_invoice_id",
+    )
+    readonly_fields = ("created", "last_modified")
+    raw_id_fields = ("user", "company", "invoice")
+    date_hierarchy = "created"