feat(templates): migrate to Zola 0.23 and Tera 2

[forkwright]

Summary

• pin the substrate and both generated consumer gates to the official Zola 0.23.3 Linux artifact;
• migrate every Typikon template from the removed Tera 1 macro/filter dialect to collision-resistant typikon.* Tera 2 components;
• preserve Zola's engine-owned feed page set, including its include_in_feeds, ordering, and limit behavior;
• add a static dialect/pin contract and a real multilingual renderer fixture for author fallbacks, breadcrumb language, and sameAs accumulation.

This is the separately gated renderer prerequisite for #179. It intentionally does not implement or close the scoped-root-feed issue.

Why this is separate

Zola 0.22.1 does not parse or expose the include_in_feeds page field required by #179 acceptance item 4. The field is native in Zola 0.23, but that release also moves the renderer to Tera 2. A version-only bump would break Typikon's macro imports, namespace calls, removed collection/string filters, and positional test arguments.

Keeping this migration separate gives the renderer transition its own exact-head proof before feed membership semantics are layered onto refreshed main.

Compatibility contract

• theme.toml, Typikon's own gate, bin/typikon-defaults.sh, and both generated consumer gate templates agree on Zola 0.23.3 and SHA-256 f07c92607e5745268b576bd325ceef3a582aada253bb64db8d92a8a85303d958.
• The digest matches GitHub's published final-release metadata for zola-v0.23.3-x86_64-unknown-linux-gnu.tar.gz.
• Components use the collision-resistant typikon.* namespace because Tera 2 registers components globally and consumer templates can otherwise replace theme internals.
• Components receive only declared arguments. Breadcrumb callers therefore pass both config and the current page/section language explicitly.
• Consumer template overrides and removed Zola shortcodes must migrate before a consumer raises its pin. This PR changes no consumer repository.

Verification before push

• Kanon MCP structured lint: 0 violations (6 existing suppressions reported).
• git diff --check: clean.
• python3 ci/check-tera2-contract.py: pass.
• Both new checks are present in the derived ci/run-fixtures.sh --list corpus.
• bin/typikon-validate examples/sample-blog: 5/5.
• bin/typikon-validate examples/sample-shop: 11/11.
• workflow-template, release-config, consumer-schema-registry, and fixture-discovery checks: pass.
• Python AST and embedded TOML/frontmatter parsing for the renderer fixture: pass.
• Three read-only source reviews found no remaining Tera 2 or candidate-diff blocker.

No Zola build was run locally. This public repository's GitHub full-gate-build job is the required authority for actual Zola 0.23.3 parsing/rendering, including the new isolated multilingual fixture. The PR should remain draft until that exact-head gate is terminal and reviewed.

Refs #179