fix: include symbol references in file dependents

[bohe76]

Summary

• include resolved symbol edges (calls, references, type/instantiation edges) when computing file dependencies and dependents
• normalize changed file paths in codegraph affected so Windows-style paths match indexed file paths
• add regression coverage for cross-file dependents and Windows path input

Validation

• npm run build
• npx vitest run __tests__/graph.test.ts --minWorkers=1 --maxWorkers=1 --testTimeout=30000 --hookTimeout=30000 --no-file-parallelism
• manual codegraph affected checks against TypeScript fixtures returned expected test files
• full serial npx vitest run ... mostly passed, with existing Windows EBUSY temp cleanup failures in mcp-roots and mcp-initialize