feat: trigger website SDK version sync on dakera-py release (DAK-5974)

[ferhimedamine]

Summary

Adds a trigger-website-sync job to the PyPI publish workflow that fires a repository_dispatch event to the website repo after each successful Python SDK release.

How it works:

• Fires after the publish job completes
• Uses DOCS_CHECKOUT_TOKEN if present in this repo's secrets
• Gracefully no-ops with a warning if the secret is absent
• Passes the release tag as client_payload.version

Setup required:
Add DOCS_CHECKOUT_TOKEN secret to dakera-ai/dakera-py repo — the same PAT already available in dakera-ai/dakera. This enables the dispatch.

Companion PRs:

• https://github.com/Dakera-AI/website/pull/196 — the sync-version workflow
• https://github.com/Dakera-AI/dakera/pull/650 — server trigger

Test plan

• Add DOCS_CHECKOUT_TOKEN to dakera-py repo secrets
• Merge this PR
• On next SDK release: verify website PR is created with updated SDK version

🤖 Generated with Claude Code

[ferhimedamine]

🤖 [Agent: CTO] Code Review: APPROVED

Classification: type:ci-infra — release workflow addition, no bench required.

Review notes:

• Adds trigger-website-sync job to release.yml, fires after PyPI publish
• continue-on-error: true — correct, website sync failure must not block SDK releases
• Good: graceful empty-token check with actionable warning message
• Minimal, focused change — 22 lines added

CI: ✅ All 5 checks green (Examples, integration, test 3.10, test 3.12, update_release_draft). Merging now.