refactor(session-temporal): call candidate read directly

[ScriptedAlchemy]

Summary

• delete private GlobalDbPreparedCandidatePort
• have the temporal store prepare root candidate cohorts by paging directly through produce_candidates_from_request
• reuse canonical bounded pull helpers without a replacement wrapper
• preserve budgets, pagination, cancellation, hydration and typed store failures

Tests

• session-temporal-store: 151 passed
• added manual-loop equivalence, budget-exceeded and cancellation tests
• affected check/clippy and formatting passed

Part of #1088.

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Latest commit: 2eea228

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[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-09T01:47:52.323137Z	2eea228	PR opened

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