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/sessions/route.ts

@@ -0,0 +1,30 @@
+import { NextResponse } from "next/server";
+import { z } from "zod";
+import { listSessions, startSession } from "@/lib/db/queries/sessions";
+import { withRouteLogging } from "@/lib/api/with-route-logging";
+
+const deviceInputSchema = z.object({
+  slotLabel: z.string().min(1),
+  bleName: z.string().min(1),
+  deviceClass: z.string().nullish(),
+  capabilities: z.object({ outputs: z.array(z.string()), featureCount: z.number() }).optional(),
+});
+
+const bodySchema = z.object({
+  name: z.string().min(1).optional(),
+  devices: z.array(deviceInputSchema).min(1),
+});
+
+export const GET = withRouteLogging("sessions.list", async () => {
+  const rows = await listSessions();
+  return NextResponse.json({ sessions: rows });
+});
+
+export const POST = withRouteLogging("sessions.start", async (req: Request) => {
+  const parsed = bodySchema.safeParse(await req.json().catch(() => null));
+  if (!parsed.success) {
+    return NextResponse.json({ error: parsed.error.message }, { status: 400 });
+  }
+  const result = await startSession(parsed.data);
+  return NextResponse.json(result, { status: 201 });
+});