PPSA v1.5.1

v1.5.1 — Palworld REST API dashboard fix

Fixes WebUI dashboard stuck indefinitely on "starting"/empty-metrics state.
Root cause: Palworld dedicated-server REST API (thijsvanloef/palworld-server-docker)
binds 127.0.0.1-only inside its own container netns, unreachable from webui's
separate netns on the same bridge network.

Fix: palworld-rest-proxy sidecar (alpine/socat, shares palworld's netns via
network_mode: "service:palworld") relays 0.0.0.0:18212 -> 127.0.0.1:8212.
webui's PALWORLD_API_URL now points at palworld:18212. No change to webui's
own ports/firewall/networking; no new port exposed to host.

Verified live on a genuinely fresh installer-ISO install: /api/dashboard
now transitions from server_state:"starting" (empty metrics) to
server_state:"running" (live FPS/player/uptime metrics) once Palworld
finishes starting — this transition never happened before the fix.

Also includes two E2E-tester fixes found during that verification pass:
- scripts/ppsa-installer-e2e.py --basefolder flag (VM/disk defaults to
  H:\dev\palimage\vms instead of filling the host C: drive)
- discover_guest_ip() fallback for --ssh-target (documented limitation:
  does not work on this appliance since it ships without VBox Guest
  Additions — --ssh-target remains required for a fully unattended run)