[rooms] fix slow room role query

apps/rooms/migrations/0029_room_role.sql

@@ -0,0 +1,31 @@
+-- Index a room's `Roles` by account, so "rooms this account has a role in"
+-- (`getContributedRooms`) is a lookup instead of a scan.
+--
+-- Roles live in the room blob, and the only way to ask "which rooms name account N" of
+-- the blob is a `json_each` over every room's `$.Roles`: the whole table, every blob
+-- parsed, on every call. `room_role` is a DERIVED copy of those entries, one row per
+-- (account, room). The blob stays the source of truth; every write in
+-- `packages/domain/src/rooms-db.ts` that changes `Roles` batches `roomRoleWrites` with it.
+--
+-- Every entry with an `AccountId` counts, pending invites (`InvitedRole` only) included,
+-- which is exactly what the json_each query matched.
+
+CREATE TABLE IF NOT EXISTS room_role (
+	account_id INTEGER NOT NULL,
+	room_id INTEGER NOT NULL,
+	PRIMARY KEY (account_id, room_id)
+) WITHOUT ROWID;
+
+CREATE INDEX IF NOT EXISTS idx_room_role_room ON room_role (room_id);
+
+-- Backfill from the rooms already stored. A full rebuild rather than an append, so this can
+-- be re-run as-is to catch role changes made by the old code between migrating and deploying.
+-- Non-object entries are skipped through a CASE rather than handed to json_extract, which
+-- raises on a bare string.
+DELETE FROM room_role;
+INSERT OR IGNORE INTO room_role (account_id, room_id)
+SELECT account_id, room_id FROM (
+	SELECT CASE WHEN role.type = 'object' THEN json_extract(role.value, '$.AccountId') END AS account_id,
+	       room.room_id AS room_id
+	FROM room, json_each(room.data, '$.Roles') AS role
+) WHERE account_id > 0 AND room_id IS NOT NULL;