Install the deployment venv with uv

[mikelangmayr]

• requires-python = ">=3.7" was not just stale, it made the project unresolvable: camera_daemon requires >=3.10, which pip ignored and uv enforces. Corrected to the floor the dependencies actually impose.
• install.sh installs a pinned uv and replaces python3 -m venv plus pip install -e with uv lock --upgrade then uv sync. Upgrading the lock first keeps the current behaviour, where a reinstall is how a merged libby fix reaches a host.
• uv.lock is gitignored for now. It still records which commits a host resolved to, so "which libby is this daemon running" becomes a file read; committing it is a separate decision for when both hosts have to match.
• .python-version pins 3.14, which is what the deployment venv already runs, and CI moves from 3.12 onto it so the daemons stop running an interpreter nothing tests.
• UV_NO_MANAGED_PYTHON=1, because the installer runs as root and the daemons run as hispec: a uv-managed interpreter would land under root's home where they could not read it.
• README replaced instructions that do not work: there is no dev extra and no requirements.txt.
• Verified locally: resolves 43 packages, pins libby 549800a and bamboo bf6403a which is exactly what the host installed on 2026-10-06, builds a venv at an arbitrary UV_PROJECT_ENVIRONMENT with bin/python3, and produces the hispec, libby and keygrabber console scripts from an editable install.

[prkrtg]

uv!!