Fix logging format: use request path instead of file path, clean timestamp

- Log request paths (/big-file.mkv) instead of file system paths
- Custom timestamp format: YYYY-MM-DDTHH:MM:SSZ (no milliseconds)
- Update serve_file to accept request parameter for proper logging
- Strip gemini://host prefix from logged requests for cleaner logs
- Add time crate for custom timestamp formatting

Cargo.toml

@@ -15,6 +15,7 @@ toml = "0.8"
 serde = { version = "1.0", features = ["derive"] }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "ansi"] }
+time = "0.3"
 
 [dev-dependencies]
 tempfile = "3"