fix: restore V3 HTTP observability

Project one typed HttpExecutionObservation per logical V3 execution through a
closed composition-root projector: only registered diagnostic context keys and
bucketed values reach the sinks, and terminal non-abort failures now emit
exactly one api.request.failed telemetry event. Caller cancellation and scope
fencing record a diagnostic but never a failure event.

routeId becomes a required input at the installed operation-executor boundary
so the feature gateway's low-cardinality route identity survives to the sink.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/integration/http-execution-contract.test.ts

@@ -98,7 +98,7 @@ describe("HTTP operation execution contract", () => {
       executor.execute(
         nonKeyedCommand,
         { name: "created" },
-        { scope, intent },
+        { routeId: "TEST_ROUTE", scope, intent },
       ),
     ).resolves.toMatchObject({ kind: "SUCCESS" });
     expect(observedKeys).toEqual([null]);
@@ -109,7 +109,7 @@ describe("HTTP operation execution contract", () => {
       executor.execute(
         nonKeyedCommand,
         { name: "created" },
-        { scope, intent: { ...intent, idempotencyKey: "unexpected-key" } },
+        { routeId: "TEST_ROUTE", scope, intent: { ...intent, idempotencyKey: "unexpected-key" } },
       ),
     ).resolves.toMatchObject({
       kind: "CONTRACT_VIOLATION",