fix: normalize Windows paths to forward slashes

[kehoej]

Closes #8

Summary

• Add filepath.ToSlash() in scanner.scanFile() so all file paths stored in the database use forward slashes regardless of OS
• Add filepath.ToSlash() to 4 locations in the Python resolver where filepath.Join() produces resolved paths, matching the pattern already used by Go, TypeScript, Java, and Rust resolvers

Root Cause

On Windows, filepath.Rel() returns backslash-separated paths (core\orchestrator\live_runtime.py), which get stored directly in SQLite. All lookup commands (analyze, get_context, analyze-change) normalize user input to forward slashes before querying, causing exact-match lookups to always fail on Windows.

Test plan

• make check (vet + lint + test) — all pass
• go test -race on all affected packages — no races
• End-to-end: built binary, indexed + analyzed contextception (Go), httpx (Python), zulip (Python monorepo)
• Verified zero backslash paths in files and edges tables across all test repos