Add current_period tracking to subscriptions, document prediction engine, and refactor station list UI

Add current_period_start, current_period_end, and stripe_data columns to subscriptions table via migration. Extend Subscription model with datetime casts for new fields. Create comprehensive prediction engine documentation covering signals, aggregation, confidence calibration, and weekly summary logic. Add PredictionFull Vue component displaying action label, reasoning, and 7-day context. Refactor StationList to collapse outdated stations behind expandable section. Add UpsellBanner component with station count formatting. Create .claude/settings.json denying .env file access. Add todo.md tracking Stripe dashboard setup, production deployment steps, and E2E QA checklist. Update .env.example with fuel-finder credentials, Anthropic config, and complete Stripe price IDs.

.claude/settings.json

@@ -0,0 +1,24 @@
+{
+    "permissions": {
+        "deny": [
+            "Read(./.env)",
+            "Read(.env)",
+            "Bash(cat .env)",
+            "Bash(cat ./.env)",
+            "Bash(head .env)",
+            "Bash(head ./.env)",
+            "Bash(tail .env)",
+            "Bash(tail ./.env)",
+            "Bash(less .env)",
+            "Bash(less ./.env)",
+            "Bash(more .env)",
+            "Bash(more ./.env)",
+            "Bash(grep * .env)",
+            "Bash(grep * ./.env)",
+            "Bash(rg * .env)",
+            "Bash(rg * ./.env)",
+            "Bash(awk * .env)",
+            "Bash(awk * ./.env)"
+        ]
+    }
+}