release: harden v0.2.0 packaging and installed CLI

[yigitcan-ozturk]

What changed

• add a v0.2.0 changelog covering the development line since v0.1.0
• explicitly mark GitHub release publication as pending while package metadata is already 0.2.0
• extend CI with an end-to-end installed-wheel smoke test outside the repository checkout
• exercise CSV ingestion, JSON decision output, deterministic explanations, provenance and XLSX report export through the installed rfqdiff CLI

Why

The v0.2 feature roadmap is implemented. Release hardening should now verify the artifact users install, not only the source checkout used during unit tests.

Release boundary

This PR does not add new scoring criteria or change recommendation semantics. It prepares the current 0.2.0 package line for publication and pilot use.