fix: normalize path separators for import graph on Windows

[hamb3r]

Problem

On Windows, os.path.relpath() returns paths with backslashes (src\myproject\core.py), but all import resolution methods (_resolve_python_import, _resolve_ts_import, _resolve_rust_import, _resolve_go_import, _resolve_csharp_import) normalize candidate paths to forward slashes before looking them up in the all_files set.

This means every lookup fails on Windows:

all_files = {'src\myproject\utils.py', 'src\myproject\core.py'}   # backslashes from os.path.relpath
candidate = 'src/myproject/utils.py'                                # forward slashes from resolvers
candidate in all_files → False                                      # always misses

As a result, import_graph and reverse_import_graph are always empty {} on Windows. This silently breaks:

• get_file_dependencies / get_file_dependents MCP tools
• get_change_impact analysis (misses cross-file impact via imports)
• The integration test test_index_mcp_codebase_index_source

CI runs on ubuntu-latest where os.sep is /, so the bug was never caught.

Root cause

Four calls to os.path.relpath() in project_indexer.py produce OS-native separators that become dict keys in ProjectIndex.files. The import resolvers already normalize candidates to /, but the keys they search against still contain \ on Windows.

Fix

Append .replace(os.sep, "/") to every os.path.relpath() call in project_indexer.py, so that file path keys are always forward-slash-normalized regardless of platform:

• Line 116 — index() main loop
• Line 191 — reindex_file()
• Line 284 — remove_file()
• Line 347 — _discover_files()

This is a one-character-class fix (4 lines changed), zero new logic. All existing import resolvers already expect forward-slash paths, so they start working correctly with no further changes.

Test plan

• All 4 previously failing tests now pass on Windows:
  • TestImportGraph::test_python_import_resolution
  • TestImportGraph::test_reverse_import_graph
  • TestImportGraph::test_typescript_relative_import
  • TestIntegration::test_index_mcp_codebase_index_source
• Full test suite: 375 passed, 0 failed
• ruff check src/ tests/ — all checks passed
• No behavior change on Linux/Mac (os.sep is already /, so .replace("/", "/") is a no-op)