feat(P3.3): OTel bridge + idempotency fidelity fixes it surfaced

AttestoSpanProcessor (attesto.otel / @attesto/sdk) turns ended OTel spans
into commitment events: source_ref otel:{trace_id}:{span_id} so resending
a span is idempotent, only allowlisted attributes committed (as a
commitment, never raw — non-allowlisted values provably absent from
stored objects), fail-open with onError, strict opt-in. Both
implementations are structurally compatible with the SpanProcessor
interface, so neither SDK gains an opentelemetry dependency.

Building this surfaced two real gaps, fixed in all three languages:
- Emulators now deduplicate on (source_kind, source_ref) like real
  ingestion (resend returns the existing receipt; anonymous empty refs
  exempt) — previously a resend silently appended a duplicate event.
- P1.6 head tracking treated an exact idempotent replay (same seq_no AND
  same event_hash as the stored head) as a fork; it is now a benign no-op,
  while same-seq/different-hash remains AttestoForkDetected (regression
  tests in Python, TypeScript-path via emulator test, and Go).

Suites: Python 109 passed, TypeScript 77 passed, Go 4/4 packages ok.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

cmd/attesto/report_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"strings"
 	"testing"
 
@@ -27,8 +28,9 @@ func TestArticle12ReportWordingAndStructure(t *testing.T) {
 		t.Fatal(err)
 	}
 	for i := 0; i < 2; i++ {
+		// Distinct source refs: identical refs are one event (idempotent ingestion).
 		if _, err := client.LogEvent(ctx, stream.StreamID, attesto.EventInput{
-			SourceRef: "e", EventType: decision.EventType(), Payload: payload,
+			SourceRef: fmt.Sprintf("e-%d", i), EventType: decision.EventType(), Payload: payload,
 		}); err != nil {
 			t.Fatal(err)
 		}