chore: adopt ecosystem qualification

[stefan-jansen]

Summary

• add standardized issue forms, pull request intake, and security reporting guidance
• add the shared Python and operating-system qualification workflow
• make release publication depend on shared qualification
• align package metadata and documentation configuration with ecosystem policy

Verification

• 3,608 tests passed before the policy assertions were updated; the focused policy suite then passed.
• workflow YAML parsed successfully

Closes #41

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[stefan-jansen]

The shared runner and repository-specific Python 3.15 dependency fixes are now on this branch. Final qualification is tracked in ml4t/ecosystem#2 and remains blocked by the accepted upstream Polars datetime failure (pola-rs/polars#28347, fix PR #28750). This PR must remain open until its current stable matrix and all three Python 3.15 prerelease jobs pass.

[stefan-jansen]

Qualification at 77b0dec is complete: 20 checks pass, including every Python 3.12-3.14 Linux, macOS, and Windows job. The three Python 3.15 prerelease jobs fail in Polars 1.43.2. The NumPy 2.5.2 Windows wheel issue is resolved. Release remains blocked by ml4t/ecosystem#2.

[stefan-jansen]

Qualification policy update: this branch now declares Requires-Python >=3.12,<3.15 and references the approved python-315-polars exception. Python 3.12-3.14 remains blocking on Linux, macOS, and Windows. The exception is version-scoped, validated by the shared workflow, tracked in ml4t/ecosystem#2, and expires on 2026-09-30. Python 3.15 qualification becomes blocking again when the upstream Polars fix is released, and no later than the expiration date.