docs: add v2.2.0 release notes

[saurabhhhcodes]

Summary

• add dedicated v2.2.0 release notes for the Smart Model Selection release scope
• cover feature highlights, configuration, examples, upgrade steps, compatibility, and limitations
• keep maintainer caveat that implementation status should be confirmed before npm publishing

Validation

• npm run build
• git diff --check

Fixes #34

[saurabhhhcodes]

Hi @Ruthwik000, this PR is clean and validated with npm run build plus git diff --check. If the release notes fit issue #34, could you please add the GSSoC scoring labels when reviewing? Suggested labels: gssoc'26, gssoc:approved, level1, documentation, and feature: smart-routing.