feat(finance): Phase 5 — Rules Engine

Add rules engine with CRUD API, condition/action evaluation, and apply-all endpoint.
UI: rule builder form with field/operator/value conditions, tag multi-select, apply button with result stats.

prisma/migrations/0005_rules/migration.sql

@@ -0,0 +1,12 @@
+CREATE TABLE IF NOT EXISTS rules (
+  id SERIAL PRIMARY KEY,
+  owner_id INTEGER NOT NULL REFERENCES participants(id),
+  name TEXT NOT NULL,
+  conditions JSONB NOT NULL DEFAULT '[]',
+  actions JSONB NOT NULL DEFAULT '{}',
+  enabled BOOLEAN NOT NULL DEFAULT true,
+  priority INTEGER NOT NULL DEFAULT 0,
+  created_at TIMESTAMPTZ DEFAULT NOW(),
+  updated_at TIMESTAMPTZ DEFAULT NOW()
+);
+CREATE INDEX IF NOT EXISTS idx_rules_owner ON rules(owner_id);