u64deck v1.9.0-rc.16 — Finder, SID Stop and diagnostics fixes

v1.9.0 Release Candidate 16

RC16 is a small, contained follow-up to RC13 — no new features, just fixes for a
handful of niggles found while using the published candidate day-to-day.

What's fixed:

• Finder no longer stalls on stale remembered addresses. Previously, if your
  config.json had old device addresses in it, a network scan could sit through a
  full timeout phase before the fresh scan even started. Remembered addresses are
  now checked as part of the same fast scan pass as everything else — a stale
  entry costs nothing. Opening the Finder also pauses background polling
  immediately so the scan gets the network to itself.
• Stop actually stops the SID. Pressing Stop in the Jukebox now cuts browser
  audio instantly instead of letting a few seconds of buffered tail play out
  while the machine resets behind it.
• Diagnostics export is cleaner. In browsers that support it you now get a
  proper save-location picker, and the success message only appears once the
  file is genuinely written. Everything sensitive stays redacted as before.
• Connect feedback. You'll see "Connecting…" the moment you pick a device,
  and the success message tells you how long it took.

Everything from RC13 — Mount & Run on both input paths, split Ethernet/Wi-Fi
routing, cartridge-safe SID Stop — is unchanged and re-verified on hardware.

Known issue: running the Ultimate with both Ethernet and Wi-Fi enabled
can make control intermittently unreliable — the firmware delays wired REST
responses by ~2.5 s in this state, and u64deck's split routing reduces but
can't eliminate the effect. For reliable operation, enable a single
interface (ideally Ethernet-only: disable Wi-Fi in the Ultimate's network
settings, then power-cycle). See the README for details.

Still a release candidate: if you hit anything odd, please report it via
Issues. u64deck.exe below is built by CI from this tag; if you prefer to run
from source, grab the code and use start.bat.