Record the theme version on generated PDFs

[sehkone]

Closes #33. Stacked on #39 — based on sehkone/issue-38, because both change build-docs-pdf.sh and tests/pdf-test.sh. Merge #39 first and this rebases to a clean diff.

Why

Both places the installed version is recorded are deliberately kept out of the build: docs/theme/.meta is dot-prefixed so MkDocs drops it, and docs/theme.toml is in exclude_docs. That exclusion is right — theme machinery should not be published — but it left nothing in a generated PDF saying which theme rendered it.

A site is a git log away from that answer. A PDF is handed to a reader and leaves the repository that produced it, and once four projects bump the theme on their own schedules the answer stops being inferable at all.

What the cover carries

docs-theme 1.2.3          # a downloaded install
docs-theme (local build)  # a --source install, ko: docs-theme (로컬 빌드)

Two decisions worth flagging:

• The value comes from .meta, not theme.toml. .meta records what is installed; theme.toml records only what was requested. Reading the latter would let a drifted or hand-edited tree misreport itself as a release.
• A --source install does not print its version. That number came from theme.toml and never resolved a release, so printing it would assert something untrue. It names the build instead.

A missing .meta is an error. A cover that quietly omits the line is the same class of silent asset loss as the 404 stylesheets this whole effort started from.

It reaches the template through extra, the way cover_tagline does, and is overwritten rather than honoured if a consumer sets it — this is derived, not configured.

Verification

tests/pdf-test.sh gains three checks, all passing:

• a --source build renders the local marker and not a version number
• rewriting .meta to source = "release" makes the cover print docs-theme 1.2.3, and the local marker disappears — this is what proves the value is read from .meta
• removing .meta fails the build with the file named

Also: both samples build --strict, shellcheck and markdownlint-cli2 clean.

Note

scripts/ci-build-pdf.py builds the sample PDFs directly from templates/ and shared/ rather than through an installed docs/theme/, so sample covers render without the line — the {% if %} guard in the template handles it. It is repo-internal and not part of the consumer surface, so it is left alone.