feat(core): add workspace_id to session table (anomalyco#15410)

Author: jlongster

packages/opencode/migration/20260227213759_add_session_workspace_id/migration.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `session` ADD `workspace_id` text;--> statement-breakpoint
+CREATE INDEX `session_workspace_idx` ON `session` (`workspace_id`);