fix(ci): pin docs-deploy to Python 3.12

[celefthe]

Follow-up to #105

After merging #105, the workflow failed again on the same push — a third, previously-masked layer of the same underlying issue (see run 31113516131):

× Failed to build `av==15.0.0`
╰─▶ pkg-config could not find libraries ['avformat', 'avcodec', ...]
hint: `av` (v15.0.0) was included because `mesoscopy` depends on `av`

--group docs (from #105) correctly installs the mesoscopy project itself, but that also pulls in the project's own runtime dependencies (av, napari, pyqt5, etc., from pyproject.toml's [project.dependencies]). uv python install with no version argument installs the latest Python (3.14 on the runner), and av==15.0.0 has no prebuilt wheel for cp314 (only up to cp313), so uv tries to build it from source — which fails because the runner has no ffmpeg dev headers.

This is the same wheel-availability problem as the original lxml issue, just one layer deeper. The Build & Test workflow already proves this exact dependency set installs cleanly on Python 3.12/3.13 (it runs a ["3.12", "3.13"] matrix on every push).

Fix

       - name: Set up Python
-        run: uv python install
+        run: uv python install 3.12

       - name: Deploy docs
-        run: uv run --no-default-groups --group docs mkdocs gh-deploy --force --clean --verbose
+        run: uv run --python 3.12 --no-default-groups --group docs mkdocs gh-deploy --force --clean --verbose

Verification

uv run --python 3.12 --no-default-groups --group docs mkdocs build --verbose exits 0 locally — installs cleanly (prebuilt wheels for av etc. on 3.12), mesoscopy imports, all pages including the CLI reference build.

🤖 Generated with Claude Code