Initial GH Copilot instructions

Author: ipspace

.github/copilot-instructions.md

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+## Review Philosophy
+
+- Only comment when you have HIGH CONFIDENCE (>80%) that an issue exists
+- Be concise: one sentence per comment when possible
+- Focus on actionable feedback, not observations
+- When reviewing text, only comment on clarity issues if the text is genuinely confusing or could lead to errors.
+
+## Skip These (Low Value)
+ 
+Do not comment on:
+
+- **Style/formatting** - CI handles this (rustfmt, prettier)
+- **Test failures** - CI handles this (full test suite)
+- **Missing dependencies** - CI handles this (mypy will fail)
+- **Minor naming suggestions** - unless truly confusing
+- **Suggestions to add comments** - for self-documenting code
+- **Multiple issues in one comment** - choose the single most critical issue
+- **Pedantic accuracy in text** - unless it would cause actual confusion or errors. No one likes a reply guy