chore: release v4.5.0

[hogan-yuan]

Release v4.5.0.

Bumps the workspace version 4.4.3 → 4.5.0 and closes out the [Unreleased] CHANGELOG section as [4.5.0] - 2026-08-14.

Included since v4.4.3

• Added: AI Agent public_agents, parent_message_id, further_questions, richer Reference payload, ChatStartedPayload fields, and Interrupt.interactions / QuestionOption.label (all languages incl. C++).
• Changed: all SDKs share a single process-wide reqwest::Client.
• Fixed: TradeContext/QuoteContext reconnect-loop leak on drop; a batch of Java JNI safety fixes (no more JVM aborts on bad args / callback failures / double-close / use-after-free).

NOT included

• Grid trading was reverted (Revert "feat(trade): Add grid trading APIs (#563)" #568) and is intentionally excluded — it will ship in a later release once the gateway is live (restore PR feat(trade): Re-land grid trading APIs (after gateway release) #570).

To publish after merge

1. Fast-forward the release branch to this commit: git push origin <merge-sha>:release (triggers the Release workflow → crates.io / PyPI / npm / Maven Central / S3).
2. Tag: git tag v4.5.0 <merge-sha> && git push origin v4.5.0.