feat: lifecycle trends migration (#10066)

Adding a single table to capture all lifecycle trends data.

One field presents a challenge: `median_time_in_stage_days`. This value
is calculated per `stage`, not per `flag_type`. As a result, we would
need to duplicate the total median time across each flag type. This
isn’t a major issue.

An alternative would be to create a separate table solely for the median
values, but that seems like overkill.

src/migrations/20250530103216-lifecycle-trends.js

@@ -0,0 +1,23 @@
+'use strict';
+
+exports.up = function(db, cb) {
+    db.runSql(
+        `
+            CREATE TABLE IF NOT EXISTS lifecycle_trends (
+                id TEXT NOT NULL,
+                stage TEXT NOT NULL CHECK (stage IN ('initial','develop', 'production', 'cleanup', 'archived')),
+                flag_type TEXT NOT NULL CHECK (flag_type IN ('experimental', 'release', 'permanent')),
+                project VARCHAR(255) NOT NULL REFERENCES projects (id) ON DELETE CASCADE,
+                flags_older_than_week INTEGER DEFAULT 0,
+                new_flags_this_week INTEGER DEFAULT 0,
+                created_at TIMESTAMP DEFAULT now(),
+                PRIMARY KEY (id, stage, flag_type, project)
+                );
+        `,
+        cb,
+    );
+};
+
+exports.down = function(db, cb) {
+    db.runSql('DROP TABLE IF EXISTS lifecycle_trends;', cb);
+};