docs: simplify build + zrepl.github.io publishing (#913)

This PR simplifies how we build and publish docs:

- **Publish from `master` branch, retire `stable` branch.** The `stable`
branch was a manual step in the release process and often out of date.
Docs are now built and published directly from `master`.
Release-specific docs are available in the `zrepl-noarch.tar` asset on
each GitHub release.

- **build dependencies**: use `uv` for dependency management

- **zrepl.github.io: retire multi-version docs**: before this PR we used
`sphinx-multiversion` to publish multiple docs versions to
`zrepl.github.io`. This was never worth the pain, so, this PR removes it
in order to simplify stuff. Old docs are available in the GitHub
releases, and the docs now have a version dropdown that links there for
a hand-curated set of versions.

- **GitHub pages repo checkout**: use HTTPS because that's what I use
these days for all things GitHub. Switch CircleCI to a fine-grained PAT.

Refs
- docs bug https://github.com/zrepl/zrepl/issues/895
  - links to config examples should work again after this PR

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/conf.py

@@ -31,10 +31,10 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['sphinx.ext.todo',
+extensions = [
+    'sphinx.ext.todo',
     'sphinx.ext.githubpages',
     'sphinx.ext.extlinks',
-    "sphinx_multiversion",
 ]
 
 # suppress_warnings = ['image.nonlocal_uri']
@@ -53,7 +53,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = 'zrepl'
-copyright = '2017-2023, Christian Schwarz'
+copyright = '2017-2026, Christian Schwarz'
 author = 'Christian Schwarz'
 
 # The version info for the project you're documenting, acts as replacement for
@@ -61,9 +61,9 @@ author = 'Christian Schwarz'
 # built documents.
 #
 # The short X.Y version.
-#version = set by sphinxcontrib-versioning
+version = 'latest'
 # The full version, including alpha/beta/rc tags.
-#release = version
+release = 'latest'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
@@ -75,7 +75,7 @@ language = 'en'
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This patterns also effect to html_static_path and html_extra_path
-exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
+exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', '.venv']
 
 # The name of the Pygments (syntax highlighting) style to use.
 pygments_style = 'sphinx'