chore: refactor hardcoded values to constants (v0.5.1)

Major internal refactoring to eliminate hardcoded values and improve
maintainability. Guardian now fully passes its own quality checks!

Changes:
- Extract all RepositoryViolation messages to domain constants
- Extract all framework leak template strings to centralized constants
- Extract all layer paths to infrastructure constants
- Extract all regex patterns to IMPORT_PATTERNS constant
- Add 30+ new constants for better maintainability

New files:
- src/infrastructure/constants/paths.ts (layer paths, patterns)
- src/domain/constants/Messages.ts (25+ repository messages)
- src/domain/constants/FrameworkCategories.ts (framework categories)
- src/shared/constants/layers.ts (layer names)

Impact:
- Reduced hardcoded values from 37 to 1 (97% improvement)
- Guardian passes its own src/ directory checks with 0 violations
- All 292 tests still passing (100% pass rate)
- No breaking changes - fully backwards compatible

Test results:
- 292 tests passing (100% pass rate)
- 96.77% statement coverage
- 83.82% branch coverage

packages/guardian/src/domain/entities/DependencyGraph.ts

@@ -94,7 +94,7 @@ export class DependencyGraph extends BaseEntity {
         totalDependencies: number
         avgDependencies: number
         maxDependencies: number
-        } {
+    } {
         const nodes = Array.from(this.nodes.values())
         const totalFiles = nodes.length
         const totalDependencies = nodes.reduce((sum, node) => sum + node.dependencies.length, 0)