fix(tests): use numeric id fixtures in flow-config schema tests

[viethung0o0]

Summary

main fails pnpm test in @chatbotx.io/flow-config. #1069 anchored zodBigintAsString to /^\d+$/, and #1104 updated the worker and business fixtures that broke — but eight flow-config test files still carry the old "step-1"-shaped ids and now fail validation (26 tests across 8 files).

This PR is fixtures only — no production code changes.

Changes

Only ids that a zodBigintAsString() schema field validates are changed; fields that are plain z.string() (template.id, nodeId, edge ids, image ids) are left as they are.

• appointment-scheduling-schema.test.ts — step id and calendarId → numeric
• import-export.test.ts — condition step id, otherwiseId and case id in the fixture flow → numeric
• messenger-template.test.ts — step id and button id (plus the matching toMatchObject assertion) → numeric
• openai-compatible-ai-steps.test.ts — aiAgentId → numeric (both the accept and reject cases, so the reject case fails for the intended reason)
• send-multiple-images.test.ts, tiktok-text-rules.test.ts, wa-template-mpm-rules.test.ts, wa-template-quick-reply-buttons.test.ts — step id → numeric

Test plan

• pnpm --filter @chatbotx.io/flow-config test — 35 files, 437 tests
• pnpm --filter builder test — 407 files, 2726 tests
• pnpm turbo run test --continue — every other workspace green
• pnpm lint
• pnpm --filter @chatbotx.io/flow-config check-types