Add agent-friendly issue templates, changelog rule, and PR template enhancements

[gerchowl]

Description

Add new issue templates, a Cursor rule for changelog updates, and enhance the PR template to close the agent workflow loop — ensuring coding agents (Cursor, Copilot, etc.) can properly handle commits, changelog entries, and pull requests end-to-end.

Problem Statement

Currently, coding agents have no guidance on:

• When and how to update CHANGELOG.md — the contributing guide documents this, but agents don't read it unless instructed. There is no Cursor rule for changelog updates.
• What changelog category to use — issue templates don't signal whether a change is "Added", "Fixed", "Changed", etc.
• Structured inputs for common work types — refactoring, documentation, and CI/build changes all funnel through the generic "Task" template, losing important context (scope boundaries, invariants, target workflows).
• Blank issue prevention — without a config.yml, users can bypass all structured templates.

Proposed Solution

1. New Cursor rule: .cursor/rules/changelog.mdc (always applied)

• When to update CHANGELOG.md (which commit types, when to skip)
• Where to update (only ## Unreleased, correct category heading)
• Entry format (bold title, issue link, sub-bullets)
• Relationship to the issue template's Changelog Category field

2. Changelog Category dropdown on all issue templates

• Added to bug_report.yml (default: Fixed), feature_request.yml (default: Added), task.yml (full list)
• Gives agents a direct signal at issue-read time

3. New issue templates

• refactor.yml — files in scope, out of scope, invariants/constraints, acceptance criteria
• documentation.yml — encodes docs/templates/ + just docs workflow, target files, doc type
• ci_build.yml — target workflows/actions, trigger types, release pipeline impact

4. Template chooser: .github/ISSUE_TEMPLATE/config.yml

• Disables blank issues
• Links to project documentation

5. Enhanced PR template

• New Changelog Entry section (paste the actual entry for review)
• Added "CI / Build change" to type of change options
• Updated checklist wording to reference docs/templates/ and just docs

Acceptance Criteria

• .cursor/rules/changelog.mdc created and always applied
• changelog-category dropdown added to bug_report.yml, feature_request.yml, task.yml
• config.yml template chooser created
• refactor.yml, documentation.yml, ci_build.yml issue templates created
• pull_request_template.md enhanced with Changelog Entry section
• CHANGELOG.md updated under ## Unreleased / ### Added