phase 3 review: fix broken error classification, stub checks, wasted uuid, token idempotency, dead code

- actuator/ssh.go: custom errorsAs chain broken — all SSH errors classified as SSHErrorOther.
  Replaced with standard errors.As + errors.Is.
- scheduler/scheduler.go: all four check functions were stubs returning healthy.
  Implemented real HTTP GET, TCP dial, unix.Statfs disk, and TLS cert expiry checks.
- learning/learning.go: uuid.NewV7() called unconditionally before ON CONFLICT upsert.
  Now looks up existing pattern first, reuses entity_id.
- notifier/notifier.go: removed dead var_, fixed token regeneration every 15s.
  Now skips if token_hash already set.
- phase3.go: removed dead GetPattern+dummy args call in PatchPattern.
- classify.go: removed unused var_ guard.

internal/policy/classify.go

@@ -155,7 +155,4 @@ func computeBlastRadius(ctx context.Context, dbc interface {
 		}
 	}
 	return ids
-}
-
-// Ensure domain is used
-var _ = domain.ErrAutonomyBlocked
+}