Add full sortof codebase: API, drain workers, frontend, schema, specs

init/07_mod_parsed_is_addon.sql

@@ -0,0 +1,7 @@
+-- Marks a mod_id as an "optional add-on" within a multi-mod wsid, signaled
+-- by `Optional add-on` (or close variants) at the head of the mod.info
+-- description. Spec A's branch picker treats addon mods additively
+-- (default-off, tickable to load alongside the primary) instead of as a
+-- mutually-exclusive flavor variant.
+ALTER TABLE mod_parsed
+    ADD COLUMN IF NOT EXISTS is_addon BOOLEAN NOT NULL DEFAULT FALSE;