[DOCS] Create PR template router at /pull_request_template.md

[ashleyshaw]

Replace generic pull_request_template.md with smart routing guide that directs users to correct template based on branch type.

Details

• GitHub will always show root template first since it doesn't support auto-routing
• Make this a helpful guide, not a boilerplate
• Detect branch name from PR (user paste into form)
• Provide quick links to all 10 PR templates
• Explain why template selection matters for automation

Content Sections

1. Header: "Which PR template should I use?"
2. Branch detection: "Your branch: feat/my-feature → use pr_feature.md"
3. Quick reference table (type/template pairs)
4. Links to all templates in PULL_REQUEST_TEMPLATE/
5. Explanation of automation (labeling, changelog, etc.)

Acceptance Criteria

• File is clear and user-friendly
• All 10+ PR templates are linked
• Branch-to-template mapping is explicit
• File explains why correct template matters

Metadata

Issue Type: Task
Priority: High
Phase: 2 - Documentation & Guidance
Effort: 1h
Depends on: #2

Project: Template Enforcement & Governance

[linear-code]

LS-857

[ashleyshaw]

Status Update: Backlog published to develop ✅

Template enforcement project backlog is now live. This issue is Phase 2 (Documentation) and depends on Phase 1 completion (#709–#711).

Complete backlog: .github/projects/active/template-enforcement-governance/ISSUES.md
Action plan: .github/projects/active/template-enforcement-governance/ACTIONS.md

Phase 2 work unblocks Phase 3 issues (#717–#720).

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