[Bug]: High CPU/disk usage when indexing large generated data folders

### Which fff frontend?

MCP server (fff-mcp)

### has logs

_No response_

### Description

`fff-mcp` caused sustained high CPU and disk usage on Windows after it encountered a large generated data folder with many files.

After quitting/disabling `fff-mcp`, system performance returned to normal.

Expected behavior:
- Large/generated folders should not cause prolonged system slowdown.
- Indexing should be throttled, skipped, or easy to exclude.

Suggested fixes:
- Add folder exclusions.
- Auto-skip very large/high-file-count folders.
- Limit concurrent indexing work.
- Show which path is currently being indexed.

No file or test is named in the issue. Start by reproducing the sustained CPU and disk usage on Windows with fff-mcp while indexing a large generated folder, then trace the indexing entry point and measure which work persists. Done means large or excluded folders no longer cause prolonged slowdown, with a clear way to identify or limit indexing work.

Written by the indexing model from the issue text.