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/stats/SessionsSummaryCards.tsx

@@ -4,7 +4,7 @@ export interface SessionsSummary {
   count: number;
   totalDurationMs: number;
   avgDurationMs: number;
-  byKind: { kind: "live" | "replay"; count: number; totalDurationMs: number }[];
+  totalReplays: number;
   durationPerDevice: { deviceId: number; displayName: string | null; bleName: string; totalActiveMs: number }[];
 }
 
@@ -13,9 +13,6 @@ function formatHours(ms: number): string {
 }
 
 export function SessionsSummaryCards({ summary }: { summary: SessionsSummary }) {
-  const liveCount = summary.byKind.find((k) => k.kind === "live")?.count ?? 0;
-  const replayCount = summary.byKind.find((k) => k.kind === "replay")?.count ?? 0;
-
   return (
     <div className="flex flex-col gap-4">
       <div className="grid gap-4 sm:grid-cols-3">
@@ -41,9 +38,7 @@ export function SessionsSummaryCards({ summary }: { summary: SessionsSummary })
         </Card>
       </div>
       <Card className="bp-glass">
-        <CardContent className="py-3 text-sm text-muted-foreground">
-          {liveCount} live · {replayCount} replay
-        </CardContent>
+        <CardContent className="py-3 text-sm text-muted-foreground">Replayed {summary.totalReplays}×</CardContent>
       </Card>
       {summary.durationPerDevice.length > 0 && (
         <Card className="bp-glass">