Replace pip with uv for yt-dlp management in Termux

[Copilot]

Swap pip out for uv as the Python package manager for yt-dlp on Termux/Android.

Changes

• setup.sh: Install uv via standalone installer, source its env immediately so it's available in the same shell session, then use uv tool install --upgrade "yt-dlp[default]" (preserves the idempotent upgrade behaviour of the old pip install -U)
• .profile: Update update-all alias — replaces pip install -U yt-dlp with uv tool upgrade yt-dlp
• README.md: Update "pip packages" → "uv packages"

# Before
yes | pip install -U "yt-dlp[default]"

# After
curl -LsSf https://astral.sh/uv/install.sh | sh
source "$HOME/.local/bin/env"
uv tool install --upgrade "yt-dlp[default]"

yt-dlp is installed as a uv-managed tool into an isolated venv, with the binary exposed at ~/.local/bin/yt-dlp — no changes needed to the downloader scripts.