feat: implement segment OR groups with ruleSets and conditions

apps/api/drizzle/0002_segment-or-groups.sql

@@ -0,0 +1,18 @@
+CREATE TYPE "public"."segment_match" AS ENUM('all', 'any');--> statement-breakpoint
+ALTER TABLE "segments" ALTER COLUMN "rules" SET DEFAULT '[[]]'::jsonb;--> statement-breakpoint
+ALTER TABLE "segments" ADD COLUMN "match" "segment_match" DEFAULT 'all' NOT NULL;--> statement-breakpoint
+/*
+ * Hand-written: drizzle-kit emits the DDL above but cannot know that `rules`
+ * changed SHAPE, from a flat condition list to a list of AND-groups. The new
+ * DEFAULT only applies to rows inserted from here on, so every existing row
+ * still holds a flat list and has to be wrapped into a single group.
+ *
+ *   []          ->  [[]]        one empty group: still matches everyone
+ *   [c1, c2]    ->  [[c1, c2]]  one group of two ANDed conditions
+ *
+ * With `match` defaulting to 'all', a single group evaluates exactly as the flat
+ * list did, so no segment changes meaning. `lib/snapshot.ts` unwraps the
+ * single-group case back to a bare `conditions` array when it writes the
+ * snapshot, which is what keeps content hashes from churning.
+ */
+UPDATE "segments" SET "rules" = jsonb_build_array("rules");