refactor: extract all hardcoded values to constants (v0.8.1)

Fix all 63 hardcoded value issues from Guardian self-check:
- Remove hardcoded Slack token from documentation
- Remove aws-sdk framework leak from domain layer
- Rename 4 pipeline files to verb-noun convention
- Extract 57 magic strings to SecretExamples.ts constants
- Update SecretViolation, SecretDetector, MagicStringMatcher
- Use typeof for TypeScript literal type in getSeverity()

Result: 0 issues in Guardian self-check (was 63)
All 566 tests passing, build successful

packages/guardian/src/application/use-cases/pipeline/CollectFiles.ts

@@ -0,0 +1,66 @@
+import { IFileScanner } from "../../../domain/services/IFileScanner"
+import { SourceFile } from "../../../domain/entities/SourceFile"
+import { ProjectPath } from "../../../domain/value-objects/ProjectPath"
+import { REGEX_PATTERNS } from "../../../shared/constants"
+
+export interface FileCollectionRequest {
+    rootDir: string
+    include?: string[]
+    exclude?: string[]
+}
+
+export interface FileCollectionResult {
+    sourceFiles: SourceFile[]
+}
+
+/**
+ * Pipeline step responsible for file collection and basic parsing
+ */
+export class CollectFiles {
+    constructor(private readonly fileScanner: IFileScanner) {}
+
+    public async execute(request: FileCollectionRequest): Promise<FileCollectionResult> {
+        const filePaths = await this.fileScanner.scan({
+            rootDir: request.rootDir,
+            include: request.include,
+            exclude: request.exclude,
+        })
+
+        const sourceFiles: SourceFile[] = []
+
+        for (const filePath of filePaths) {
+            const content = await this.fileScanner.readFile(filePath)
+            const projectPath = ProjectPath.create(filePath, request.rootDir)
+
+            const imports = this.extractImports(content)
+            const exports = this.extractExports(content)
+
+            const sourceFile = new SourceFile(projectPath, content, imports, exports)
+            sourceFiles.push(sourceFile)
+        }
+
+        return { sourceFiles }
+    }
+
+    private extractImports(content: string): string[] {
+        const imports: string[] = []
+        let match
+
+        while ((match = REGEX_PATTERNS.IMPORT_STATEMENT.exec(content)) !== null) {
+            imports.push(match[1])
+        }
+
+        return imports
+    }
+
+    private extractExports(content: string): string[] {
+        const exports: string[] = []
+        let match
+
+        while ((match = REGEX_PATTERNS.EXPORT_STATEMENT.exec(content)) !== null) {
+            exports.push(match[1])
+        }
+
+        return exports
+    }
+}