Fix 7 corner cases found in second review pass

Critical:
- Persist serverProtocol/ts6ApiKey in database schema so TS6 config
  survives restarts (added columns + manager save/load)

Medium:
- Clear udpErrorTimer on disconnect to prevent memory leak and stale
  log messages from firing after teardown
- Guard against double connect() by disconnecting old client first
- Add settled guard in TS6HttpQuery.request() to prevent double
  reject when both res error and req error fire
- Add res.on("error") handler to TS6HttpQuery response stream

Low:
- Cap probeTS3Query banner buffer at 256 bytes to prevent memory abuse
  from non-TS3 services sending large data on port 10011
- Remove unnecessary EventEmitter inheritance from TS6HttpQuery
- Update database test fixtures with new serverProtocol/ts6ApiKey fields

https://claude.ai/code/session_016WhH58avUD9xy2dgADJgTh

src/ts-protocol/protocol-detect.ts

@@ -67,11 +67,13 @@ function probeTS3Query(host: string, port: number, timeoutMs: number): Promise<b
 
     const socket = net.createConnection({ host, port, timeout: timeoutMs });
     let banner = "";
+    const MAX_BANNER = 256; // TS3 banner is ~50 bytes; cap to avoid memory abuse
 
     socket.setTimeout(timeoutMs);
 
     socket.on("data", (data: Buffer) => {
       banner += data.toString("utf-8");
+      if (banner.length > MAX_BANNER) banner = banner.slice(0, MAX_BANNER);
       if (banner.includes("TS3")) {
         done(true);
       }