test: add sample Slint file and test results template

Add test files for manual verification of the Slint LSP integration:
- hello.slint: Sample Slint component with common UI elements
- TEST_RESULTS.md: Checklist template for testing LSP features

Co-Authored-By: Claude (auto) <noreply@anthropic.com>

test-files/TEST_RESULTS.md

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+# Slint LSP Integration Test Results
+
+Date: 2026-01-29
+
+## Test Environment
+- IntelliJ IDEA: 2025.2.4
+- Slint LSP Version: 1.14.1
+- Plugin Version: 1.0-SNAPSHOT
+
+## Test Results
+
+### File Type Recognition
+- [ ] .slint files show Slint icon
+- [ ] File type is recognized as "Slint"
+
+### Syntax Highlighting
+- [ ] Keywords highlighted (import, export, component, inherits)
+- [ ] Strings highlighted
+- [ ] Comments highlighted
+- [ ] Properties highlighted
+
+### LSP Features
+- [ ] LSP server starts automatically
+- [ ] Code completion works
+- [ ] Hover documentation works
+- [ ] Goto definition works
+- [ ] Diagnostics show errors/warnings
+- [ ] Code formatting works
+- [ ] Find references works
+- [ ] Rename refactoring works
+
+## Issues Found
+(Document any issues here)
+
+## Notes
+(Any additional observations)