Prepare v1.1 release metadata

[SteveDiamond]

Summary

• keep the project license as GPLv3 and update the README license text to match the existing LICENSE/package metadata
• update release-facing docs for the build workflow badge and CVXPY 1.9.0 minimum
• fix workflow branch triggers for master and correct the label sync path
• remove a stale sdist include for a missing NOTICE file

Verification

• uv run pre-commit run check-toml --all-files
• uv run pre-commit run check-yaml --all-files
• uv run pre-commit run yamllint --all-files
• uv build
• inspected wheel metadata: License GPLv3, GPLv3 classifier, cvxpy>=1.9.0