ci: port the Cloudflare Workers docs pipeline to circinus (slug 1.5) (#2208)

* ci: port Cloudflare Workers docs pipeline files to circinus (verbatim)

Copies the branch-agnostic half of the docs.vyos.io Cloudflare Workers
pipeline from `rolling` at 8cb568bf, byte-identical:

  - .github/workflows/docs-build.yml
  - workers/ (entire tree)
  - scripts/docs_gates/
  - docker/im-convert.sh
  - docs/_static/js/version-picker.js, js/pagefind-wrapper.js,
    css/version-picker.css (new files, no circinus counterpart)
  - docs/_templates/breadcrumbs.html, searchbox.html (new files)

docs-build.yml already triggers on push to [rolling, circinus, sagitta]
and resolves `circinus` -> worker vyos-docs-v15-en / slug 1.5 from
workers/matrix.json; the files simply did not exist on this branch, so
slug 1.5 still serves the bootstrap placeholder.

workers/versions.json + workers/matrix.json are deliberately identical
across all three branches and must be kept in sync.

Advances: IS-572

* ci: wire circinus docs build into the Cloudflare Workers pipeline

Hand-merges the CF-specific hunks onto circinus's own docker/Dockerfile
and docs/conf.py rather than clobbering them with rolling's versions —
circinus keeps its own content-driven history in both files.

docker/Dockerfile:
  - imagemagick + librsvg2-bin (sphinx.ext.imgconverter backend) and
    poppler-utils (pdfinfo, used by docs-build.yml's PDF page-count
    completeness check), installed --no-install-recommends
  - install docker/im-convert.sh as /usr/local/bin/im-convert

docs/conf.py:
  - enable sphinx.ext.imgconverter + image_converter = 'im-convert' so
    the LaTeX/PDF builder stops silently dropping .webp/.svg images
  - register js/version-picker.js + css/version-picker.css
    unconditionally (degrades silently on ReadTheDocs)
  - _vyos_cf_build gate off the raw DOCS_VERSION_SLUG env var; only CF
    builds load js/pagefind-wrapper.js, and html_context['vyos_cf_build']
    lets _templates/searchbox.html fall back to the stock Sphinx
    searchbox via the "!" bang-include on RTD

The RTD path stays the default in both files: circinus continues
building on ReadTheDocs until RTD sunset, and every CF feature activates
only when DOCS_VERSION_SLUG is present. .readthedocs.yml is untouched.

circinus keeps its own version/release/html_title/source_suffix and its
hardcoded html_baseurl (its CF slug is also `1.5`, so rolling's
DOCS_VERSION_SLUG/READTHEDOCS_VERSION resolution block is a no-op here
and was deliberately not ported).

Advances: IS-572

* ci: IS-572: re-sync ported Cloudflare Workers pipeline files with rolling

The category-1 files in this port are byte-identical copies from `rolling`.
`rolling` has since moved: [vyos-documentation#2209](https://github.com/vyos/vyos-documentation/pull/2209)
merged as `3a1c6c30`, thirteen rounds of hardening on exactly these files.

Re-take all 14 category-1 paths from `origin/rolling` via
`git checkout origin/rolling -- <paths>`, so byte-identity holds by
construction rather than by hand-editing:

  .github/workflows/docs-build.yml
  scripts/docs_gates/{gates,parity,smoke,test_gates,test_parity,test_smoke}.py
  workers/.gitignore
  workers/apex/src/{index,special,uagate}.ts
  workers/apex/test/{router,uagate}.test.ts
  workers/apex/ua-policy.json

Thirteen of the fourteen carry
[vyos-documentation#2209](https://github.com/vyos/vyos-documentation/pull/2209)
exactly — the pre-change tree was byte-identical to `3a1c6c30^` for those
paths. `workers/.gitignore` additionally picks up the one-line `test-results/`
entry from
[vyos-documentation#2212](https://github.com/vyos/vyos-documentation/pull/2212);
inert on circinus, since only the deliberately-unported `apex-deploy.yml`
writes that directory.

Deliberate exclusions are unchanged: `docs-canary-qa.yml` (cron runs on the
default branch only, so it is not ported even though
[vyos-documentation#2209](https://github.com/vyos/vyos-documentation/pull/2209)
touched it on `rolling`), `apex-deploy.yml`, and the `docs-preview-*`
workflows. `docs/conf.py` stays hand-merged and circinus-specific, with its
ReadTheDocs fallback intact.

🤖 Generated by [robots](https://vyos.io)

1 files changed, 55 insertions, 0 deletions

diff --git a/scripts/docs_gates/conftest.py b/scripts/docs_gates/conftest.py
new file mode 100644
index 00000000..38d6127e
--- /dev/null
+++ b/scripts/docs_gates/conftest.py
@@ -0,0 +1,55 @@
+"""Shared pytest fixtures for docs_gates tests.
+
+Provides a real local HTTP server (stdlib http.server, no TLS) used to exercise the
+_NoRedirect opener pattern (parity.py / smoke.py) end-to-end over an actual network
+round trip, rather than only unit-testing the handler class in isolation.
+"""
+from __future__ import annotations
+
+import threading
+from collections.abc import Iterator
+from http.server import BaseHTTPRequestHandler, HTTPServer
+
+import pytest
+
+REDIRECT_PATH = "/redirect-me"
+REDIRECT_LOCATION = "https://example.invalid/target"
+
+
+class _RedirectHandler(BaseHTTPRequestHandler):
+    """301+Location for REDIRECT_PATH; 200 for anything else."""
+
+    def do_GET(self) -> None:  # noqa: N802 — stdlib handler method name
+        self._respond()
+
+    def do_HEAD(self) -> None:  # noqa: N802
+        self._respond()
+
+    def _respond(self) -> None:
+        if self.path == REDIRECT_PATH:
+            self.send_response(301)
+            self.send_header("Location", REDIRECT_LOCATION)
+            self.end_headers()
+        else:
+            self.send_response(200)
+            self.send_header("Content-Type", "text/plain")
+            self.end_headers()
+            if self.command == "GET":
+                self.wfile.write(b"ok")
+
+    def log_message(self, format: str, *args: object) -> None:  # noqa: A002 — quiet test output
+        pass
+
+
+@pytest.fixture
+def redirect_http_server() -> Iterator[str]:
+    """Starts the server on 127.0.0.1 (ephemeral port); yields 'host:port'."""
+    server = HTTPServer(("127.0.0.1", 0), _RedirectHandler)
+    thread = threading.Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    try:
+        yield f"127.0.0.1:{server.server_address[1]}"
+    finally:
+        server.shutdown()
+        server.server_close()
+        thread.join(timeout=5)