feat(db): add migration 002 for updated_at trigger and enabled index

Adds auto-update trigger for updated_at column on adapters table
and partial index for efficient enabled adapter queries.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sql/migrations/002_add_updated_at_trigger_and_index.sql

@@ -0,0 +1,21 @@
+-- Migration: 002_add_updated_at_trigger_and_index
+-- Adds auto-update trigger for updated_at column on adapters table
+-- Adds partial index for efficient enabled adapter queries
+
+-- Auto-update trigger for updated_at
+CREATE OR REPLACE FUNCTION config.set_updated_at()
+RETURNS trigger AS $$
+BEGIN
+    NEW.updated_at := now();
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER adapters_set_updated_at
+    BEFORE UPDATE ON config.adapters
+    FOR EACH ROW EXECUTE FUNCTION config.set_updated_at();
+
+-- Partial index for enabled adapters (common query pattern)
+CREATE INDEX adapters_enabled_idx
+    ON config.adapters (enabled)
+    WHERE enabled = true;