docs: add Paimon Rust 0.2.0 release note

[luoyuxia]

Summary

• Add release note for Paimon Rust 0.2.0
• Covers 59 commits (54 from 12 human contributors + 5 dependabot)
• Key features: primary key table write, partial-update merge engine, Vortex format, Blob type, Lumina vector index, system tables, expanded DML/DDL SQL surface

Test plan

• Verify markdown renders correctly on the website
• Cross-check feature descriptions against paimon-rust release-0.2 branch

🤖 Generated with Claude Code

[luoyuxia]

@JingsongLi Could you please help review when you got time