merge: Phase 5 (Rules Engine) + Phase 6 (Budget & Analytics)

Resolve additive conflicts in schema.prisma and hooks.ts — both models and all hooks retained.

prisma/migrations/0006_budgets/migration.sql

@@ -0,0 +1,11 @@
+CREATE TABLE IF NOT EXISTS budgets (
+  id SERIAL PRIMARY KEY,
+  owner_id INTEGER NOT NULL REFERENCES participants(id),
+  category TEXT NOT NULL,
+  month DATE NOT NULL,
+  amount_limit NUMERIC(10,2) NOT NULL,
+  created_at TIMESTAMPTZ DEFAULT NOW(),
+  updated_at TIMESTAMPTZ DEFAULT NOW(),
+  UNIQUE(owner_id, category, month)
+);
+CREATE INDEX IF NOT EXISTS idx_budgets_owner_month ON budgets(owner_id, month);