v0.43.0: canonical systemd unit + publish agent binary + golden to Gitea (BUNDLE slice)

- configs/felhom-agent.service: canonical non-root unit (User=felhom-agent, sudo model);
  deliberately NO NoNewPrivileges (breaks sudo) and NO mount-namespacing hardening (breaks
  the intermediary-mount drive propagation into guests) — documented inline.
- scripts/publish-agent.sh: build (optional) + PUT binary to Gitea generic + sha256 +
  GET round-trip. Pinned version, idempotent (delete-then-PUT).
- configs/build-golden.sh: after vzdump, compute sha256 + PUT golden.tar.zst to Gitea
  generic (version = baked controller version). Opt-in; local auto-discovery stays fallback.
- cmd/felhom-agent/main.go: version 0.42.0 -> 0.43.0.
- README: process model now canonical (non-root + publish/install).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/felhom-agent/main.go

@@ -44,7 +44,7 @@ import (
 
 // version is the agent version. Overridable at build time with
 // -ldflags "-X main.version=<v>"; defaults to the in-repo CHANGELOG version.
-var version = "0.42.0"
+var version = "0.43.0"
 
 // runGuestHook is the PVE pre-start hook body (`felhom-agent guest-hook <vmid> <phase>`). On the
 // pre-start phase it creates placeholder dirs for any absent bind-mount source so the guest always boots