chore: improve GenAI tests in PR descriptions

[ovitrif]

This PR improves the shared /pr instructions so AI-generated PR descriptions split QA notes into focused manual validation and visible automated check coverage.

Description

This PR:

1. Requires generated QA notes to use ### QA Notes with #### Manual Tests and #### Automated Checks.
2. Adds a concrete manual-test template with unchecked boxes, bold numbering, navigation arrows, regression labels, and variation sub-lists.
3. Routes automated commands, test suites, and CI coverage notes into the automated-checks section, including the workflow (after merge) caveat.
4. Moves durable /pr and /release command specs into .agents/commands while keeping .claude/commands as a compatibility symlink.

Preview

N/A

QA Notes

Manual Tests

• 1. Repo checkout → inspect .claude/commands: pr.md and release.md resolve through the symlink.
• 2. Agent docs → open AGENTS.md: durable PR command behavior points to .agents/commands/pr.md.
• 3. /pr --dry in Claude Code → generate a PR body: QA Notes contains separate Manual Tests and Automated Checks sections.

Automated Checks

• git diff --check

[jvsena42]

LGTM