refactor(run-engine): make taskIdentifier optional on run-queue messages (#3559)

## Summary

Make `taskIdentifier` optional on the run-queue message schema. No
behavior change in this PR; readers continue to accept payloads that
include the field. A separate change will stop writing it on the wire to
shrink the per-run payload that lives in Redis while runs wait to be
dequeued.

## Design

The field is written into every payload at enqueue time but no consumer
reads it back on the dequeue path. Both the run-engine and supervisor
derive `taskIdentifier` from the loaded `TaskRun` row instead. Relaxing
the schema first means readers tolerate payloads that omit it, so the
writer-side change can ship without producing schema-parse errors during
a rolling deploy.

`projectId` is left required: `WorkerQueueResolver.#getOverride` reads
it for project-scoped runtime worker-queue overrides.

## Test plan

- [x] `pnpm run typecheck --filter @internal/run-engine`
- [x] `pnpm run typecheck --filter webapp`
- [x] `pnpm run test ./src/run-queue/tests/enqueueMessage.test.ts
./src/run-queue/tests/workerQueueResolver.test.ts --run` (28/28 passing)

internal-packages/run-engine/src/run-queue/types.ts

@@ -4,7 +4,8 @@ import type { MinimalAuthenticatedEnvironment } from "../shared/index.js";
 
 export const InputPayload = z.object({
   runId: z.string(),
-  taskIdentifier: z.string(),
+  /** Deprecated: not read on the V2 dequeue path; will stop being written in a follow-up. Optional to keep new readers compatible with old payloads that still include it, and vice versa. */
+  taskIdentifier: z.string().optional(),
   orgId: z.string(),
   projectId: z.string(),
   environmentId: z.string(),