core: rename session entry to message and expose full session lifecycle events in SDK

Renamed SessionEntry to SessionMessage for clearer, more intuitive API terminology
that better represents the message-based nature of session interactions.

Exposed 22 new session lifecycle event types in the JavaScript SDK including
prompted, step started/ended, text/reasoning/tool deltas, tool calls with
progress tracking, retries, and compaction events. This enables SDK consumers
to build real-time UIs that accurately reflect agent session state as it evolves,
providing users with visibility into thinking steps, tool execution, and retries.

Author: thdxr

packages/opencode/migration/20260427172553_slow_nightmare/migration.sql

@@ -0,0 +1,17 @@
+CREATE TABLE `session_message` (
+	`id` text PRIMARY KEY,
+	`session_id` text NOT NULL,
+	`type` text NOT NULL,
+	`time_created` integer NOT NULL,
+	`time_updated` integer NOT NULL,
+	`data` text NOT NULL,
+	CONSTRAINT `fk_session_message_session_id_session_id_fk` FOREIGN KEY (`session_id`) REFERENCES `session`(`id`) ON DELETE CASCADE
+);
+--> statement-breakpoint
+DROP INDEX IF EXISTS `session_entry_session_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `session_entry_session_type_idx`;--> statement-breakpoint
+DROP INDEX IF EXISTS `session_entry_time_created_idx`;--> statement-breakpoint
+CREATE INDEX `session_message_session_idx` ON `session_message` (`session_id`);--> statement-breakpoint
+CREATE INDEX `session_message_session_type_idx` ON `session_message` (`session_id`,`type`);--> statement-breakpoint
+CREATE INDEX `session_message_time_created_idx` ON `session_message` (`time_created`);--> statement-breakpoint
+DROP TABLE `session_entry`;