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/0002_add_session_replay_fields.sql

@@ -0,0 +1,4 @@
+ALTER TABLE `play_sessions` ADD `description` text;--> statement-breakpoint
+ALTER TABLE `play_sessions` ADD `replayed_session_id` integer REFERENCES play_sessions(id) ON DELETE SET NULL;--> statement-breakpoint
+ALTER TABLE `play_sessions` ADD `play_count` integer DEFAULT 0 NOT NULL;--> statement-breakpoint
+ALTER TABLE `play_sessions` ADD `last_played_at` integer;