feat(web,myra): a mailed package can carry a cron schedule; Deploy creates the scheduled workflow (CL-8513)

[TheGreatAxios]

Summary

• deployable-package.ts now parses an optional schedule (a five-field cron string) on definition.json, validated by field count only (no third-party cron parser).
• The Deploy card shows the human sentence from cronSentence(schedule) under the name, or a clear error when the schedule isn't a valid five-field string (Deploy stays disabled in that case).
• agent-deploy.ts adds a stock { type: "schedule", cron } trigger alongside the existing { type: "mail", to } trigger when schedule is set — the same trigger shape vendor/intx/workflow/src/live-inert-projector.ts projects for case "schedule". NewAgentInput and useDeployAgentMutation thread schedule through as an optional key, omitted when undefined.
• Myra's system prompt now mentions the optional five-field cron schedule in the same sentence as package.json/definition.json.

The deployment still lists on the Workflows page through the existing stock GET /workflows/deployments read; routines-api.ts's cron: "manual" placeholder is unchanged since stock's deployment listing still doesn't expose trigger data.

Test plan

• bunx tsc -p apps/web --noEmit
• bun run lint
• bun run fmt
• cd apps/web && bun run build
• cd apps/web && bun test ./src (582 pass)

[linear-code]

CL-8513