[deps] Bundle ltchiptool for libretiny prebuilt-dir uploads

`esphome upload --prebuilt-dir` on a libretiny device routes through
ltchiptool to bypass the PlatformIO build-tree requirement. On hosts
that have never compiled a libretiny config locally (the dashboard's
transparent-install use case) the libretiny PlatformIO platform's
penv at ~/.platformio/penv/.libretiny/bin/ltchiptool doesn't exist
yet, leaving the upload to fail with an actionable but unwelcome
"install ltchiptool" hint.

Bundle ltchiptool as a direct dependency, mirroring esptool which is
already shipped even though only ESP users need it. `pip install
esphome` is now sufficient for libretiny serial uploads from a
prebuilt artifact set; get_ltchiptool_path's PATH lookup picks up
the pip-installed binary first, with the PIO penv fallback still in
place for environments that vendor esphome without the extra.

Issue: esphome/device-builder#572
Issue: esphome/device-builder#570

requirements.txt

@@ -10,6 +10,7 @@ tzdata>=2026.2  # from time
 pyserial==3.5
 platformio==6.1.19
 esptool==5.2.0
+ltchiptool==4.14.1
 click==8.3.3
 esphome-dashboard==20260425.0
 aioesphomeapi==44.23.0