Sync project SDLC files with bootnode-sdlc starter-kit #472

User story / Problem statement

Currently, several project SDLC files have drifted from or lag behind the bootnode-sdlc starter-kit. Legacy issue and PR templates coexist with the newer structured ones, the PR template is missing guidance hints and subsections present in the starter-kit, CLAUDE.md is missing a "no related issue" guidance note, and the feature/epic templates lost their Priority dropdowns.

Expected outcome

The project's SDLC files match the current starter-kit state: legacy templates removed, PR template updated with all starter-kit content, CLAUDE.md aligned with the PR workflow guidance, and feature/epic issue templates restored with the Priority dropdown.

Acceptance criteria

• Remove pull_request_template.md from project root (superseded by .github/PULL_REQUEST_TEMPLATE.md)
• Remove .github/ISSUE_TEMPLATE/bug_report.md (superseded by 1-bug.yml)
• Remove .github/ISSUE_TEMPLATE/feature_request.md (superseded by 2-feature.yml)
• Add <!-- Or: No related issue. <motivation> --> hint after Closes # in .github/PULL_REQUEST_TEMPLATE.md
• Split ## Test plan into ### Automated tests and ### Manual verification subsections in .github/PULL_REQUEST_TEMPLATE.md
• Add ## Screenshots section (defaulting to None.) to .github/PULL_REQUEST_TEMPLATE.md
• Add "No related issue?" guidance note to the PR Workflow section in CLAUDE.md
• Restore Priority dropdown to .github/ISSUE_TEMPLATE/2-feature.yml
• Restore Priority dropdown to .github/ISSUE_TEMPLATE/3-epic.yml