docs: convert issue templates to YAML forms, add PR template

.github/ISSUE_TEMPLATE/0repository-bug-report.yml

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+name: Repository bug report
+description: Create a report to help us improve the RVC3-python repository
+labels: ["bug"]
+assignees: ["petercorke"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        This report is for bugs with the **RVC3-python repo itself**: missing files,
+        incorrect documentation, broken links, notebooks that won't run, etc.
+
+        Reports related to a specific software component used in the book should be
+        reported on that component's own issues page instead — they will not be
+        actioned if posted here:
+
+        - [Robotics Toolbox for Python](https://github.com/petercorke/robotics-toolbox-python/issues)
+        - [Machine Vision Toolbox for Python](https://github.com/petercorke/machinevision-toolbox-python/issues)
+        - [Spatial Maths Toolbox for Python](https://github.com/petercorke/spatialmath-python/issues)
+        - [bdsim: block diagram simulation for Python](https://github.com/petercorke/bdsim/issues)
+        - [Swift graphical simulator for Python](https://github.com/jhavl/swift/issues)
+        - [Spatial Geometry Toolbox for Python](https://github.com/jhavl/spatialgeometry/issues)
+        - [PGraph, mathematical graph library for Python](https://github.com/petercorke/pgraph-python/issues)
+  - type: textarea
+    id: description
+    attributes:
+      label: Describe the bug
+      description: A clear and concise description of what the bug is.
+    validations:
+      required: true
+  - type: textarea
+    id: repro
+    attributes:
+      label: To reproduce
+      description: Provide the smallest possible code snippet, or exact steps, that demonstrate the error.
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected behavior
+      description: A clear and concise description of what you expected to happen.
+    validations:
+      required: true
+  - type: dropdown
+    id: os
+    attributes:
+      label: Operating system
+      description: If you're running a script from the command line.
+      options: [macOS, Linux, Windows, Other, Not applicable]
+    validations:
+      required: false
+  - type: dropdown
+    id: notebook-env
+    attributes:
+      label: Notebook environment
+      description: If this is about a Jupyter notebook.
+      options: [Google Colab, Local Jupyter, Not applicable]
+    validations:
+      required: false
+  - type: input
+    id: browser
+    attributes:
+      label: Browser
+      description: If using Colab or local Jupyter.
+      placeholder: "e.g. Chrome, Safari"
+    validations:
+      required: false
+  - type: textarea
+    id: context
+    attributes:
+      label: Additional context
+      description: Add any other context, or screenshots, about the problem here.
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/1errata.yml

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+name: Errata
+description: 'Report errors in the book: Robotics, Vision & Control 3e, in Python'
+labels: ["errata"]
+assignees: ["petercorke"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Errors in books are a nightmare for the readers and the author! If you spot
+        something that is wrong, or something that could be improved (clearer, less
+        confusing, less ambiguous) please log it here. This will help fellow readers
+        of the book, and will improve future editions of the book.
+  - type: input
+    id: page
+    attributes:
+      label: Page number
+      description: Or a figure/equation/table number if that's clearer.
+      placeholder: "e.g. 142, or 'Fig 3.5 caption'"
+    validations:
+      required: true
+  - type: textarea
+    id: location
+    attributes:
+      label: Where is the error?
+      description: >-
+        Clearly describe where on the page the issue is. Provide the existing text
+        as a reference, or specify the location relative to an equation or figure.
+    validations:
+      required: true
+  - type: textarea
+    id: error
+    attributes:
+      label: What is the error?
+      description: A clear and concise description of how you'd like to see the text changed, and why.
+    validations:
+      required: true
+  - type: textarea
+    id: context
+    attributes:
+      label: Additional context
+      description: Add any other context, or screenshots, here.
+    validations:
+      required: false

.github/pull_request_template.md

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+Thanks for contributing to RVC3-python!
+
+## Summary
+
+<!-- What does this PR do, and why? -->
+
+## Related issue
+
+<!-- Fixes #123 / Closes #123 -- if applicable -->
+
+## Checklist
+
+- [ ] Tests pass locally (`pytest tests/`, and `pytest tests/ --runall` if this touches a notebook or an `RVC3/examples` script)
+- [ ] New/changed code is type-hinted with modern syntax (`X | Y`, `list[X]`, not `Union`/`Optional`/`List`)
+- [ ] Docstrings updated (reST style: `:param:`, `:returns:`; type hints in the signature cover types now, `:type:`/`:rtype:` are rarely needed)