Bind draining payload upload retries to the current completion lease

[rmcdaniel]

Companion to durable-workflow/server#146 and durable-workflow/server#147.

• Keep ordinary uploads unchanged.
• On a draining refusal only, use Server's advertised completion-context capability for one retry with the same bytes.
• Bind task, attempt, worker owner, operation and immutable payload slot. Cover activity result/failure, query result, workflow commands/failure and stream payloads.
• Preserve old-Server behavior, client-input refusals, namespace quotas, integrity checks and terminal errors. Do not rerun handlers or add a retry coordinator.
• Prepare PHP SDK 2.0.9.

Validation: 633 tests / 3,609 assertions, one existing skip; PHPStan passes. Full PHP/framework CI passed at implementation commit 18b52e0. Real HTTP activity/workflow/query completion and cold payload readback passed against the Server fix, alongside Python and Rust: durable-workflow/server#147 (comment)

Release-metadata CI is running at the final head. Published-artifact bounded-storage qualification remains on Server #146; this PR does not claim a production deployment.