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/proxmox/tls_test.go

@@ -0,0 +1,46 @@
+package proxmox
+
+import "testing"
+
+func TestNormalizeFingerprint(t *testing.T) {
+	// 64-hex with colons (the /nodes ssl_fingerprint form) normalizes fine.
+	const withColons = "BA:7C:99:7D:45:D0:67:91:E2:F2:72:74:6E:D6:9F:83:51:D1:61:E5:C3:BD:F6:A0:B8:0B:E3:D8:DB:89:5B:CF"
+	got, err := normalizeFingerprint(withColons)
+	if err != nil {
+		t.Fatalf("normalize: %v", err)
+	}
+	if len(got) != 64 {
+		t.Errorf("len = %d", len(got))
+	}
+	if got != "ba7c997d45d06791e2f272746ed69f8351d161e5c3bdf6a0b80be3d8db895bcf" {
+		t.Errorf("got %q", got)
+	}
+}
+
+func TestNormalizeFingerprint_Bad(t *testing.T) {
+	for _, c := range []string{"", "tooshort", "zz7c997d45d06791e2f272746ed69f8351d161e5c3bdf6a0b80be3d8db895bcf"} {
+		if _, err := normalizeFingerprint(c); err == nil {
+			t.Errorf("normalize(%q) = nil, want error", c)
+		}
+	}
+}
+
+func TestTLSConfig_Build(t *testing.T) {
+	// Fingerprint pin produces a config with a pin verifier (and the documented
+	// InsecureSkipVerify=true that the verifier overrides).
+	c, err := (TLSConfig{Fingerprint: "ba7c997d45d06791e2f272746ed69f8351d161e5c3bdf6a0b80be3d8db895bcf"}).build()
+	if err != nil {
+		t.Fatalf("build pin: %v", err)
+	}
+	if c.VerifyPeerCertificate == nil {
+		t.Errorf("pin config missing VerifyPeerCertificate")
+	}
+	// Default (no trust set) uses system roots, no skip.
+	def, err := (TLSConfig{}).build()
+	if err != nil {
+		t.Fatalf("build default: %v", err)
+	}
+	if def.InsecureSkipVerify {
+		t.Errorf("default must verify")
+	}
+}