ci: restore immediate cross-repo consumer dispatch

[tiankaima-copilot]

Problem

The Server OpenAPI consumer sync workflow completes successfully but skips every cross-repository dispatch when OPENAPI_SYNC_TOKEN is absent.

Observed on main after Server 679d3be6012b3cc486e789874a6f32100adc5812:

• workflow run: https://github.com/Life-USTC/server/actions/runs/33085348888
• step warning: OPENAPI_SYNC_TOKEN is not configured; consumer dispatch was skipped.
• no Bot workflow or PR was created until the Bot sync was manually dispatched for the exact Server SHA

Bot currently has only a daily scheduled fallback (23 2 * * *), so generated clients can remain stale for nearly a day even though the Server workflow is green.

Required outcome

• Configure a dedicated GitHub App or automation token as OPENAPI_SYNC_TOKEN with the minimum permissions needed to dispatch openapi-updated to Life-USTC/bot and Life-USTC/cli.
• Verify a Server OpenAPI change immediately starts both consumer workflows with the exact 40-character Server commit SHA.
• Keep the scheduled consumer workflow as a backup.
• Make a missing dispatch credential visible as a degraded/failing automation signal rather than an indistinguishable successful sync.

Do not use a personal developer token as the long-term credential.