schema: add config.streams table with column-filtered notify

- config.streams table for JetStream retention config
- Column-filtered NOTIFY: only fires on max_age_s changes
- Prevents self-loop when supervisor updates max_bytes
- Seeds CENTRAL_WX (7d/10GB) and CENTRAL_META (1d/100MB)

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

sql/migrations/003_add_streams_table.sql

@@ -0,0 +1,46 @@
+-- Migration: 003_add_streams_table
+-- Creates the config.streams table for JetStream stream retention configuration.
+-- Uses column-filtered NOTIFY to prevent self-loop when supervisor updates max_bytes.
+
+-- Streams configuration table
+CREATE TABLE config.streams (
+    name              TEXT PRIMARY KEY,
+    max_age_s         BIGINT NOT NULL,
+    max_bytes         BIGINT NOT NULL DEFAULT 1073741824,  -- 1GB default
+    managed_max_bytes BOOLEAN NOT NULL DEFAULT true,
+    updated_at        TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+-- Auto-update trigger for updated_at
+CREATE TRIGGER streams_set_updated_at
+    BEFORE UPDATE ON config.streams
+    FOR EACH ROW EXECUTE FUNCTION config.set_updated_at();
+
+-- Column-filtered NOTIFY trigger for streams.
+-- Fires on INSERT/DELETE always.
+-- On UPDATE, only fires when max_age_s changes (operator-touchable field),
+-- NOT when max_bytes changes (supervisor-managed), to prevent recompute loop.
+CREATE OR REPLACE FUNCTION config.notify_streams_change()
+RETURNS trigger AS $$
+BEGIN
+    IF TG_OP = 'INSERT' OR TG_OP = 'DELETE' THEN
+        PERFORM pg_notify('config_changed', 'streams:' ||
+            COALESCE(NEW.name, OLD.name));
+    ELSIF TG_OP = 'UPDATE' AND
+          OLD.max_age_s IS DISTINCT FROM NEW.max_age_s THEN
+        PERFORM pg_notify('config_changed', 'streams:' || NEW.name);
+    END IF;
+    RETURN COALESCE(NEW, OLD);
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER streams_notify
+    AFTER INSERT OR UPDATE OR DELETE ON config.streams
+    FOR EACH ROW EXECUTE FUNCTION config.notify_streams_change();
+
+-- Seed with current stream values from investigation
+-- CENTRAL_WX: 7d max_age (604800s), 10GB max_bytes (will be clamped to 6GB on first recompute)
+-- CENTRAL_META: 1d max_age (86400s), 100MB max_bytes (will be raised to 1GB floor)
+INSERT INTO config.streams (name, max_age_s, max_bytes) VALUES
+    ('CENTRAL_WX',   604800,  10737418240),
+    ('CENTRAL_META', 86400,   104857600);