Fix Linear candidate query compatibility

[Octane0411]

Summary

• align the TypeScript Linear candidate queries with the upstream GraphQL shape
• include relation pagination and assignee fields needed by the real Linear workflow
• keep blocker normalization compatible with both issue and legacy sourceIssue payloads

Validation

• pnpm test tests/tracker/linear-client.test.ts tests/tracker/linear-normalize.test.ts
• pnpm build
• real workflow smoke test against /Users/wangruobing/Personal/symphony/elixir/WORKFLOW.linear-demo-oas-demo.md and a temporary variant including In Review in active_states
  • before fix: TypeScript runtime failed with Linear HTTP 400 while upstream dispatched successfully
  • after fix: TypeScript runtime dispatched the same issues as upstream in the temporary workflow smoke test