Simplify community intake

[fly1d]

Why

Community intake currently presents eight overlapping routes and requires repetitive fields before a user can ask a question or share a result. This raises the cost of the real-user feedback the project now needs. Review whether the smaller routing model keeps enough context for maintainers to act.

What changed

• Consolidate workflow feedback into Show and tell and benchmark proposals into Improvement proposals, leaving six distinct public routes.
• Reduce Q&A to two required questions, reduce result sharing to two required questions plus one optional follow-up, and reduce the pull request template to four free-form sections.
• Preserve reproduction, validation, safety, authorship, ownership, and completion context in the specialized paths and contributor contract.
• Surface the measured 854-to-11 Gradle result before installation in the README.

No reducer, CLI, report, Action, or compatibility behavior changes.

Verification

• python3 scripts/check_contribution.py -> passed: documentation, Ruff, byte compilation, and 763 unit tests; 4 platform-dependent skips.
• Ruby YAML parsing for the issue chooser and both Discussion forms -> passed.
• git diff --check -> passed.

Disclosure

• No secrets, credentials, private URLs, proprietary source, or confidential logs are included.
• Documentation and changelog entries are updated.
• Material OpenAI Codex involvement: repository audit, patch implementation, test updates, and validation. The repository owner authorized the maintenance work.