Added GitHub issue and PR templates for bugs, docs, and feature requests

.github/ISSUE_TEMPLATE/bug-report.yml

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+name: "Bug Report"
+description: "Report an expression that isn't being parsed, compared, or graded correctly."
+title: "Bug: "
+labels:
+  - bug
+assignees: []
+body:
+  - type: textarea
+    id: description
+    attributes:
+      label: Description of the bug
+      description: "What's going wrong?"
+      placeholder: |
+        e.g. sec^2(x) is rejected as an invalid expression instead of being parsed as sec(x)**2.
+    validations:
+      required: true
+
+  - type: textarea
+    id: expressions
+    attributes:
+      label: Expression(s)/input that trigger it
+      description: "The response and/or answer expression(s) that reproduce the issue."
+      placeholder: |
+        - Response: sec^2(x)
+        - Answer: sec(x)**2
+      render: markdown
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected_actual
+    attributes:
+      label: Expected vs. actual result
+      description: "What did you expect to happen, and what actually happened instead?"
+      placeholder: |
+        - Expected: marked as correct
+        - Actual: raised a parsing error / marked as incorrect
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduce
+    attributes:
+      label: Steps to reproduce / where it was used
+      description: "Optional: how you triggered it, e.g. via the eval function directly, a specific set/question, params used."
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/docs-issue.yml

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+name: "Docs Issue"
+description: "Report missing or incorrect documentation."
+title: "Docs: "
+labels:
+  - documentation
+assignees: []
+body:
+  - type: textarea
+    id: issue
+    attributes:
+      label: What's missing or incorrect
+      description: "Describe the gap or error in the documentation."
+    validations:
+      required: true
+
+  - type: input
+    id: location
+    attributes:
+      label: Location
+      description: "Where is this? e.g. app/docs.md, README, user-documentation site."
+      placeholder: "app/docs.md"
+    validations:
+      required: false
+
+  - type: textarea
+    id: suggested_fix
+    attributes:
+      label: Suggested fix
+      description: "Optional: what should it say instead?"
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/feature-request.yml

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+name: "Feature Request"
+description: "Propose new functionality or an improvement to how expressions are compared."
+title: "Feature: "
+labels:
+  - enhancement
+assignees: []
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem / use case
+      description: "What can't you currently do, and why does it matter?"
+      placeholder: |
+        e.g. Custom multi-character variable names aren't supported, so questions using
+        variables like `V_max` can't be graded correctly.
+    validations:
+      required: true
+
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed solution
+      description: "What would you like to see happen?"
+    validations:
+      required: true
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives considered
+      description: "Optional: any workarounds or other approaches you've considered."
+    validations:
+      required: false

.github/PULL_REQUEST_TEMPLATE.md

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+## Problem
+<!-- What's broken or missing, and why it matters -->
+
+## Changes
+<!-- - `path/to/file.py`: what changed and why -->
+
+## Checklist
+- [ ] Tests added/updated
+- [ ] Docs updated (`app/docs.md`) if user-facing behaviour changed
+
+Closes #