fix(routing): normalize Windows route paths

[skyswordw]

Summary

• Normalize fs.glob route discovery results to forward slashes before Pages/App Router parsing.
• Keep scanner-derived route paths normalized when storing route metadata and deriving app route segments.
• Add regression coverage that simulates Windows-style backslash glob output for both Pages Router and App Router route discovery.

Closes #1605.

Testing

• pnpm test tests/routing-windows-paths.test.ts
• pnpm test tests/routing.test.ts tests/app-route-graph.test.ts
• pnpm test tests/routing-windows-paths.test.ts tests/routing.test.ts tests/app-route-graph.test.ts
• pnpm run check
• pnpm run build
• git diff --check

Notes

Local command execution used the repository's pinned pnpm@11.1.1 with Node 24.14.0 because the machine's Homebrew Node 26 caused native dependency install failures for better-sqlite3.