docs(changelog): sv-ide v002.1 ramp landings today

[hkimw]

Summary

• Add root Keep a Changelog-style CHANGELOG.md for the 2026-05-07 v002.1 PR ramp.
• Group the stack as Status Surface (feat(kv260): add read-only status surface for IDE #124), UI Theme (feat(ui): integrate pccx-UI theme and logo #125), Preflight Binding (feat(kv260): wire preflight panel to live serial probe #126), Polish (feat(panel): polish v002.1 readiness presentation #127), Palette (feat(palette): add read-only v002.1 navigation commands #128), and Docs (docs(panel): v002.1 readiness panel developer guide #129).
• Keep the entry scoped to repository changes under review.

Validation

• git diff --check
• python3 -m pytest -q tests/test_repository_hygiene.py
• node editors/vscode-prototype/test/static-boundary.test.mjs
• python3 scripts/check-source-headers.py
• git commit hooks passed with the configured hook path
• git push completed without force

Guardrails

• Docs only.
• No marketplace flow claim.
• No stable API/ABI claim.
• No launcher execution, pccx-lab execution, serial writes, SSH, board commands, provider calls, telemetry, uploads, write-back, packaging, tag, or release flow.