refactor!: remove unapproved compatibility APIs

[stefan-jansen]

Summary

• remove PolygonProvider, the polygon registry/config name, check_negative_prices, and garch_omega for the 0.2 line
• keep the approved QLDM_DATA_ROOT and QldmError migrations, and retain POLYGON_API_KEY only as a service credential fallback
• replace the stale root API manifest and volatile Massive plan claims with current source-backed documentation
• document exact 0.2 migrations and add runtime contract tests for removed interfaces
• replace nonexistent CHANGELOG.md links with the repository release notes
• refresh the pinned ecosystem workflow so the approved Python 3.15 wait covers development versions below 0.2

Affected version

ml4t-data 0.1.8 and the 0.1 release line. The removal targets 0.2.0.

Compatibility

This is intentionally breaking and must not ship as 0.1.x. The next release containing it must be 0.2.0 or later. Migration guidance is in docs/getting-started/migration.md.

Verification

• uv run ruff check src tests scripts
• uv run ruff format --check src tests scripts
• uv run ty check
• uv run pytest tests -q -ra - 3,652 passed, 283 deselected
• uv run pytest tests -q -ra -W error::ResourceWarning - 3,652 passed, 283 deselected
• uv run mkdocs build --strict
• clean wheel and sdist build, twine check, metadata validation, isolated install, silent import, CLI help, and README quick start
• every README local and remote link checked
• actionlint .github/workflows/*.yml
• pre-commit run --all-files
• local shared exception validation against ecosystem policy snapshot 293400c

Closes #65

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.