Add issue templates, CONTRIBUTING.md, and code of conduct

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Report a problem with NotAlterra
+title: ''
+labels: bug
+assignees: ''
+---
+
+**Describe the bug**
+What happened and what did you expect to happen?
+
+**Steps to reproduce**
+1. 
+2. 
+3. 
+
+**Environment**
+- OS: (e.g. Windows 11, Ubuntu 24.04)
+- NotAlterra version: (shown in the title bar)
+- Subnautica 2 install: (Steam, Xbox, Epic, custom)
+
+**Logs**
+If available, attach `transaction.log` (located next to the binary).

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an improvement for NotAlterra
+title: ''
+labels: enhancement
+assignees: ''
+---
+
+**What problem would this solve?**
+A clear description of the pain point.
+
+**Proposed solution**
+What would you like NotAlterra to do?
+
+**Alternatives considered**
+Any workarounds or alternative approaches you've tried.
+
+**Additional context**
+Screenshots, references to other save managers, or anything relevant.