Add proactive financial intelligence feed

Shifts the AI assistant from reactive (users ask questions) to proactive
(the system surfaces personalized insights automatically). A nightly job
analyzes every family's financial data across 7 insight types, writes
natural-language explanations via Claude, and surfaces them in a feed on
the dashboard and a standalone /insights page.

Feature is behind a flag: off by default, enable with INSIGHTS_ENABLED=1
(or via Setting.insights_enabled in the admin UI).

Insight types:
- spending_anomaly: category spend >25% above/below 3-month rolling average
- cash_flow_warning: projected cash balance drops below $500 in 30 days
  (uses RecurringTransaction + statistical daily baseline)
- net_worth_milestone: crossed a round-number milestone or all-time high
- subscription_audit: recurring transaction overdue by 45+ days
- savings_rate_change: savings rate changed >5 percentage points vs last month
- idle_cash: $5k+ sitting in depository account with no activity in 60 days
- budget_at_risk / budget_on_track: spending pace vs monthly budget

Architecture:
- Insight model with dedup_key unique index (upsert, not re-create daily)
- Insight::Generator base class + Insight::GeneratorRegistry orchestrator
- LLM used as a writer only — financial math runs in pure Ruby
- GenerateInsightsJob runs at 6 AM UTC daily via sidekiq-cron
- InsightsController with read/dismiss Turbo Stream actions
- Dashboard section gated by Current.user.insights_enabled?

https://claude.ai/code/session_014vY9xohpm3abSAxVxRF27a

test/models/insight_test.rb

@@ -0,0 +1,83 @@
+require "test_helper"
+
+class InsightTest < ActiveSupport::TestCase
+  test "mark_read! transitions active to read and sets read_at" do
+    insight = insights(:spending_anomaly_dining)
+    assert insight.active?
+    assert_nil insight.read_at
+
+    insight.mark_read!
+
+    assert insight.read?
+    assert_not_nil insight.read_at
+  end
+
+  test "mark_read! is a no-op when already read" do
+    insight = insights(:net_worth_milestone)
+    assert insight.read?
+    original_read_at = insight.read_at
+
+    insight.mark_read!
+
+    assert_equal original_read_at, insight.reload.read_at
+  end
+
+  test "dismiss! transitions to dismissed and sets dismissed_at" do
+    insight = insights(:spending_anomaly_dining)
+    assert insight.active?
+
+    insight.dismiss!
+
+    assert insight.dismissed?
+    assert_not_nil insight.dismissed_at
+  end
+
+  test "visible scope excludes dismissed insights" do
+    dismissed = insights(:dismissed_insight)
+    assert_not Insight.visible.include?(dismissed)
+  end
+
+  test "visible scope includes active and read insights" do
+    active = insights(:spending_anomaly_dining)
+    read   = insights(:net_worth_milestone)
+
+    assert Insight.visible.include?(active)
+    assert Insight.visible.include?(read)
+  end
+
+  test "ordered scope places high priority before medium before low" do
+    high_insight = insights(:cash_flow_warning)      # high
+    medium_insight = insights(:spending_anomaly_dining)  # medium
+
+    ordered = Insight.where(family: families(:dylan_family)).visible.ordered
+    high_idx   = ordered.index(high_insight)
+    medium_idx = ordered.index(medium_insight)
+
+    assert_not_nil high_idx
+    assert_not_nil medium_idx
+    assert high_idx < medium_idx
+  end
+
+  test "dedup_key uniqueness is enforced per family" do
+    original = insights(:spending_anomaly_dining)
+
+    duplicate = Insight.new(
+      family:       original.family,
+      insight_type: original.insight_type,
+      priority:     "low",
+      status:       "active",
+      title:        "Duplicate",
+      body:         "Duplicate body",
+      metadata:     {},
+      currency:     "USD",
+      dedup_key:    original.dedup_key,
+      generated_at: Time.current
+    )
+
+    assert_raises(ActiveRecord::RecordNotUnique) { duplicate.save!(validate: false) }
+  end
+
+  test "for_dashboard scope returns at most 3 visible insights" do
+    assert Insight.for_dashboard.count <= 3
+  end
+end