Remove recordings feature, replay sessions directly, bump to 0.6.0

Recordings were just a thin named pointer over an already-captured
session's events, so the whole separate feature (recordings table, API
routes, pages, UI) is gone: any completed session can now be named and
replayed directly. Replaying no longer creates a session or duplicates
events of its own - it just bumps the source session's playCount/lastPlayedAt.

Also renames play_sessions/playSession(s) to sessions/session(s) throughout
the schema, queries, API routes, and UI for consistency, and updates the
README to match the new flow.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

drizzle/0003_rename_sessions.sql

@@ -0,0 +1,5 @@
+ALTER TABLE `play_sessions` RENAME TO `sessions`;--> statement-breakpoint
+ALTER TABLE `session_devices` RENAME COLUMN `play_session_id` TO `session_id`;--> statement-breakpoint
+ALTER TABLE `session_events` RENAME COLUMN `play_session_id` TO `session_id`;--> statement-breakpoint
+DROP INDEX `session_devices_play_session_id_idx`;--> statement-breakpoint
+CREATE INDEX `session_devices_session_id_idx` ON `session_devices` (`session_id`);