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>

components/control/RecordControls.tsx

@@ -20,7 +20,7 @@ export function RecordControls({ active, elapsedLabel, disabled, busy, onStart,
           <Circle className="bp-pulse size-2.5 fill-destructive text-destructive" />
           Session live · {elapsedLabel}
         </span>
-        <Button variant="outline" size="sm" onClick={onEnd} disabled={busy}>
+        <Button variant="outline" onClick={onEnd} disabled={busy}>
           <Square className="size-3.5" /> End session
         </Button>
       </div>