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>

app/api/stats/recordings/route.ts

@@ -1,8 +0,0 @@
-import { NextResponse } from "next/server";
-import { getRecordingLibraryStats } from "@/lib/db/queries/stats";
-import { withRouteLogging } from "@/lib/api/with-route-logging";
-
-export const GET = withRouteLogging("stats.recordings", async () => {
-  const stats = await getRecordingLibraryStats();
-  return NextResponse.json(stats);
-});