fix: HTTP router 404 on query params + missing first_timestamp in incremental scan

[Fruhji]

Problems

1. Dashboard returns 404 when URL has query parameters

Opening http://localhost:8080/?range=month&models=claude-sonnet-4-6 returned a 404 because do_GET compared self.path directly against "/". When the browser appends query parameters, self.path becomes /?range=... which never matched.

Fix: Parse the path with urlparse before routing so query parameters are stripped.

2. first_timestamp never updated in incremental scans

When new lines are appended to an existing JSONL file, the incremental scan updated last_timestamp correctly but never updated first_timestamp — even if a newly seen record had an earlier timestamp. This caused session duration (duration_min) to be underestimated.

Fix: Mirror the last_timestamp update logic for first_timestamp using < instead of >.