Add GitHub templates for PRs, bug reports, and feature requests

Author: Borda

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: "Bug Report"
+description: Report a bug
+title: "[Bug]: "
+labels: ["bug", "triage"]
+body:
+  - type: textarea
+    id: bug
+    attributes:
+      label: Bug description
+      description: Expected vs. actual behavior.
+    validations:
+      required: true
+  - type: textarea
+    id: steps
+    attributes:
+      label: Steps to reproduce
+      description: Minimal steps.
+      placeholder: |
+        1. ...
+        2. ...
+        See error.
+    validations:
+      required: true
+  - type: textarea
+    id: environment
+    attributes:
+      label: Environment (optional)
+      description: OS, Python, toolchain.

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: "Feature Request"
+description: Suggest a feature
+title: "[Feature]: "
+labels: ["feature", "triage"]
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem
+      description: What problem does it solve?
+      placeholder: I'm frustrated when...
+    validations:
+      required: true
+  - type: textarea
+    id: solution
+    attributes:
+      label: Solution
+      description: Describe the feature.
+    validations:
+      required: true

.github/pull_request_template.md

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+# PR Checklist
+
+- [ ] Tests pass
+- [ ] Docs if needed
+- [ ] pre-commit passes
+
+## Changes
+
+Brief description.
+
+## Related
+
+Closes #