feat: Add AI-powered Smart Test Runner system

.github/scripts/ai_test_selection_prompt.md

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+# Smart Test Selection AI Prompt
+
+You are an expert Ruby developer analyzing code changes to determine which tests should be run.
+
+## CODE CHANGES ANALYSIS
+The following files have been changed:
+{{changed_files_summary}}
+
+## CHANGE DETAILS
+```diff
+{{diff_content}}
+```
+
+## AVAILABLE TEST FILES
+{{test_files_list}}
+
+## TEST-TO-SOURCE MAPPING
+{{test_mapping}}
+
+## INSTRUCTIONS
+Analyze the changes and select tests that should be run. Consider:
+
+1. **Direct tests**: Tests that directly test the changed source files
+2. **Indirect tests**: Tests that might be affected by the changes through:
+   - Inheritance or module inclusion
+   - Dependency injection
+   - Shared interfaces or contracts
+   - Integration points
+   - Configuration changes
+
+3. **Risk assessment**: Consider the impact of changes:
+   - Public API changes → Run more tests
+   - Internal implementation → Focus on direct tests
+   - Breaking changes → Run comprehensive tests
+
+## OUTPUT FORMAT
+Respond with a JSON object in this exact format:
+```json
+{
+  "selected_tests": [
+    "spec/lib/kanban_metrics/example_spec.rb"
+  ],
+  "reasoning": {
+    "direct_tests": ["list of tests that directly test changed files"],
+    "indirect_tests": ["list of tests that might be indirectly affected"],
+    "risk_level": "low|medium|high",
+    "explanation": "Detailed explanation of selection reasoning"
+  }
+}
+```
+
+Select tests intelligently - don't run everything, but don't miss important dependencies.
+
+## RUBY-SPECIFIC CONSIDERATIONS
+
+### File Mapping Conventions
+- Source files in `lib/` correspond to test files in `spec/`
+- `lib/foo/bar.rb` → `spec/lib/foo/bar_spec.rb`
+- Class names follow CamelCase → snake_case conversion
+
+### Test Dependencies to Consider
+- **Module Inclusion**: Changes to modules affect all classes that include them
+- **Inheritance**: Changes to parent classes affect all subclasses
+- **Shared Examples**: Changes to shared examples affect all tests that use them
+- **Factory Dependencies**: Changes to factories affect tests that use them
+- **Configuration**: Changes to initializers, configs affect integration tests
+
+### Risk Level Guidelines
+- **Low Risk**: Private method changes, internal refactoring, documentation
+- **Medium Risk**: Public method signature changes, new public methods, class structure changes
+- **High Risk**: Interface changes, breaking changes, dependency updates, configuration changes
+
+### Test Selection Strategy
+- Always include direct tests for changed source files
+- For module/class changes, include tests for dependent classes
+- For configuration changes, include integration and system tests
+- For Gemfile/dependency changes, consider running full suite
+- For test-only changes, run the changed tests plus any that depend on shared examples/helpers