Docs: move submission guidance to GitHub templates (#16232)

* Docs: move submission guidance to GitHub templates

* Docs: make PR risk template entries flexible

* Docs: remove PR reviewer checklist section

.github/pull_request_template.md

@@ -0,0 +1,108 @@
+## Summary
+
+Describe the problem and fix in 2–5 bullets:
+
+- Problem:
+- Why it matters:
+- What changed:
+- What did NOT change (scope boundary):
+
+## Change Type (select all)
+
+- [ ] Bug fix
+- [ ] Feature
+- [ ] Refactor
+- [ ] Docs
+- [ ] Security hardening
+- [ ] Chore/infra
+
+## Scope (select all touched areas)
+
+- [ ] Gateway / orchestration
+- [ ] Skills / tool execution
+- [ ] Auth / tokens
+- [ ] Memory / storage
+- [ ] Integrations
+- [ ] API / contracts
+- [ ] UI / DX
+- [ ] CI/CD / infra
+
+## Linked Issue/PR
+
+- Closes #
+- Related #
+
+## User-visible / Behavior Changes
+
+List user-visible changes (including defaults/config).  
+If none, write `None`.
+
+## Security Impact (required)
+
+- New permissions/capabilities? (`Yes/No`)
+- Secrets/tokens handling changed? (`Yes/No`)
+- New/changed network calls? (`Yes/No`)
+- Command/tool execution surface changed? (`Yes/No`)
+- Data access scope changed? (`Yes/No`)
+- If any `Yes`, explain risk + mitigation:
+
+## Repro + Verification
+
+### Environment
+
+- OS:
+- Runtime/container:
+- Model/provider:
+- Integration/channel (if any):
+- Relevant config (redacted):
+
+### Steps
+
+1.
+2.
+3.
+
+### Expected
+
+-
+
+### Actual
+
+-
+
+## Evidence
+
+Attach at least one:
+
+- [ ] Failing test/log before + passing after
+- [ ] Trace/log snippets
+- [ ] Screenshot/recording
+- [ ] Perf numbers (if relevant)
+
+## Human Verification (required)
+
+What you personally verified (not just CI), and how:
+
+- Verified scenarios:
+- Edge cases checked:
+- What you did **not** verify:
+
+## Compatibility / Migration
+
+- Backward compatible? (`Yes/No`)
+- Config/env changes? (`Yes/No`)
+- Migration needed? (`Yes/No`)
+- If yes, exact upgrade steps:
+
+## Failure Recovery (if this breaks)
+
+- How to disable/revert this change quickly:
+- Files/config to restore:
+- Known bad symptoms reviewers should watch for:
+
+## Risks and Mitigations
+
+List only real risks for this PR. Add/remove entries as needed. If none, write `None`.
+
+- Risk:
+  - Mitigation: