feat: add PR and issue templates for contributor workflow (#296)

Adds structured templates to help contributors submit higher-quality
PRs and issues. PR template includes testing checklist (pytest, sync.sh).
Issue templates use YAML forms for bug reports and feature requests.

Fixes #251

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,24 @@
+name: Feature Request
+description: Suggest a new feature or improvement
+labels: [enhancement]
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem
+      description: What problem does this solve?
+      placeholder: When I try to ..., I can't ...
+    validations:
+      required: true
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed Solution
+      description: How should this work?
+    validations:
+      required: true
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives Considered
+      description: Other approaches you thought of (optional).