chore(deps): use 3-day exclude-newer window

* chore(deps): use 3-day exclude-newer window

Aligns the root workspace with the per-package pyprojects, which
already use `exclude-newer = "3 days"`. The fixed 2026-04-27 cutoff
blocks legitimate dependency bumps (e.g. daytona ~=0.171 in #5740)
without adding meaningful protection — the relative window still
includes the security patches that motivated the original pin.

* fix(deps): bump gitpython and python-multipart for new advisories

- gitpython >=3.1.49 for GHSA-v87r-6q3f-2j67 (newline injection in
  config_writer().set_value() enables RCE via core.hooksPath).
- python-multipart >=0.0.27 for GHSA-pp6c-gr5w-3c5g (DoS via
  unbounded multipart part headers).

Both surfaced via pip-audit on this branch.