release: v2.0.13 artifacts, credentials, and session guards

[wicm84266964]

Summary

• Dashboard lists script-generated plots, reports, and exports and opens the latest file in the right pane.
• Same-URL credentials are chosen automatically so chat is not blocked before send. HTTP 401/403 then asks the user to inspect or switch the active credential.
• Empty-visible-text diagnostics stay in the UI and are not written into model context.
• A one-line tool promise with no tool call is retried once after rotating gateway session affinity.
• Unsolicited Responses web_search_call events fail as a protocol mismatch instead of a silent completion.

Validation

• Local public verify:release: 1,356 unit/integration tests passed (TAP plan 1,342 plus nested), 38 browser tests passed, 0 failed, 0 skipped.
• Cross-repository parity: 34 exact paths and 12 reviewed differences.
• Candidate notes: docs/releases/2.0.13-artifacts-credentials-session-guard_zh.md.

This is the v2.0.13 public release candidate. Tag and GitHub Release follow after required CI on this PR and on main.