feat(agent): scaffold + proxmox interaction layer (slice 1)

Stand up the felhom-agent project (module gitea.dooplex.hu/admin/felhom-agent,
binary felhom-agent) and the internal/proxmox package: the typed library every
other agent module calls to talk to Proxmox.

- API-first Client (hand-rolled REST over net/http, PVEAPIToken auth) with typed
  read ops (version/nodes/status/lxc/config/storage) and async mutating ops
  (restore/vzdump/snapshot/rollback/delete-snapshot/setconfig/start/stop), each
  returning a UPID. WaitTask polls task status until stopped and asserts
  exitstatus OK (authz can surface at task exec, not the POST — phase1-2 §1.3).
- Fenced Privileged (root-CLI) backend for the THREE proven exceptions only
  (keyctl pct create, USB mount/fstab, SMART/sensors); each cites why it can't be
  the API. Fence is structural (Client never shells out, Privileged never HTTPs)
  and asserted in routing_test.go.
- TLS: SHA-256 leaf-cert pinning or CA file; insecure mode explicit + off by
  default. No blanket verification disable.
- 403 -> privilege-named APIError; failed task -> privilege-named TaskError.
- JSON config + env overrides (token never logged); slog logging.
- cmd/felhom-agent --selftest (read-only health report) + gated --selftest=task
  (reversible snapshot/rollback/delete exercise of WaitTask). No daemon loop yet.
- Types grounded in the spike findings and exact JSON shapes captured live from
  demo-felhom (PVE 9.2.2). Unit tests use a mock transport + runner.

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

internal/log/log.go

@@ -0,0 +1,28 @@
+// Package log builds the agent's slog logger. Kept tiny on purpose; the agent is
+// a host service, so logs go to stderr (journald-friendly). Secrets must never be
+// passed to the logger — config is logged only via Config.Redacted (see config).
+package log
+
+import (
+	"log/slog"
+	"os"
+	"strings"
+)
+
+// New returns a text slog.Logger at the given level ("debug"|"info"|"warn"|
+// "error"; unknown falls back to info), writing to stderr.
+func New(level string) *slog.Logger {
+	var lvl slog.Level
+	switch strings.ToLower(level) {
+	case "debug":
+		lvl = slog.LevelDebug
+	case "warn", "warning":
+		lvl = slog.LevelWarn
+	case "error":
+		lvl = slog.LevelError
+	default:
+		lvl = slog.LevelInfo
+	}
+	h := slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: lvl})
+	return slog.New(h)
+}