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/httpapi/phase3.go

@@ -850,14 +850,6 @@ func (s *Server) PatchPattern(ctx context.Context, req gen.PatchPatternRequestOb
 	}
 
 	// Re-read.
-	pat, err := q.GetPattern(ctx, sqlcgen.GetPatternParams{
-		// We need to look up by entity_id, not by applies_type+action.
-		// GetPattern uses applies_type+action as key, so fetch via raw query.
-		AppliesType: "", // dummy, will use raw query instead
-		Action:      "",
-	})
-	_ = pat
-	// Use raw query to get by entity_id
 	var p gen.Pattern
 	err = tx.QueryRow(ctx, `
 		SELECT entity_id, applies_type, action, pattern, confidence,