restore-test: verdict is liveness, not start-task exitstatus (v0.7.0)

Fixes the crying-wolf false-fail surfaced by the live hub-enrollment runbook:
PVE's guest-start task exits "WARNINGS: 1" for the benign systemd-nesting
advisory, and WaitTask treated any non-OK exitstatus as failure, so the verdict
was decided by an advisory exit code before the real boot check ran. Every
modern-distro restore-test reported pass:false.

- proxmox.WaitOptions.AllowWarnings (opt-in; default keeps all callers strict)
- restore-test start step accepts warnings, surfaces them, verdict stays waitRunning
- RestoreTestResult.StartWarnings/.WarningsRecognized + version-free "enable
  nesting" recognizer (can't rot back at systemd 258+); GuestAPI.TaskLogTail
- hub.RestoreTest.warnings/.warnings_recognized wire fields (consumed by hub v0.7.5)
- scheduler logs clean / passed-with-recognized / passed-with-unrecognized warnings
- tests: WaitTask warnings matrix; restore-test pass/fail-on-liveness; version-free
  regression guard (systemd 256-300)

Single agent bump 0.6.0 -> 0.7.0 covering the agent half of both task phases.

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

internal/reconcile/engine_test.go

@@ -29,6 +29,8 @@ type fakeAPI struct {
 	waitFunc func(upid string) (proxmox.TaskStatus, error)
 	// statusFunc backs TaskStatusOnce (crash recovery); default = stopped/OK.
 	statusFunc func(upid string) (proxmox.TaskStatus, error)
+	// logTailFunc backs TaskLogTail (restore-test start-warning surfacing); default = empty.
+	logTailFunc func(upid string) ([]string, error)
 
 	starts   []int
 	stops    []int
@@ -75,6 +77,13 @@ func (f *fakeAPI) TaskStatusOnce(_ context.Context, upid string) (proxmox.TaskSt
 	return proxmox.TaskStatus{UPID: upid, Status: "stopped", ExitStatus: "OK"}, nil
 }
 
+func (f *fakeAPI) TaskLogTail(_ context.Context, upid string, _ int) ([]string, error) {
+	if f.logTailFunc != nil {
+		return f.logTailFunc(upid)
+	}
+	return nil, nil
+}
+
 type setCall struct {
 	vmid   int
 	params map[string]string