chore(docs): use a builder-portable homepage check in the override template

[lesnik512]

Why

page.is_homepage is a MkDocs Page property with no equivalent in Zensical, which the org is
evaluating as a future docs builder (modern-python/.github#60). It fails silently, not loudly:
at Zensical 0.0.59 the property does not exist anywhere in the source, and an undefined name
resolves falsy in MiniJinja — so the home page would fall through to the non-home branch and emit a
wrong og:title / twitter:title with no warning.

nav.homepage is exposed by both builders — MkDocs documents it as homepage: Page | None
(https://www.mkdocs.org/dev-guide/themes/), and Zensical serializes it in
crates/zensical/src/structure/nav/view.rs — so comparing page.url against it is portable.

Part of modern-python/.github#71, which makes the same change in each repo with an
overrides/main.html.

Design

{%- set is_home = nav.homepage and page.url == nav.homepage.url %}, then not is_home where
not page.is_homepage used to be.

• The nav.homepage and guard is load-bearing: MkDocs types it Page | None. When it is None
  the expression is falsy, which matches is_homepage being False on every page of a site with
  no home page.
• The {%- left-trim is also load-bearing: without it the new tag adds a blank line to every
  rendered page.

Non-goals

Not a Zensical migration. #60 stays open and stays blocked on unrelated gaps (exclude_docs,
validation.omitted_files). This change is a no-op under MkDocs today and does not depend on that
work landing.

Verification

Full-site build diff with the pinned toolchain, main vs this branch:

uvx --with-requirements docs/requirements.txt mkdocs build --strict -d <dir>
diff -r <before> <after>

--strict passes on both, and the output is byte-identical across all 64 pages — including
index.html's <title>, og:title and twitter:title, which are what this touches.

[github-actions]

Benchmark

Details

Benchmark suite	Current: 04bcbb3	Previous: 032e8ec	Ratio
benchmarks/test_guard_by_type.py::test_g16_resolve_by_type	2957692.3989288416 iter/sec (stddev: 2.5378540438786837e-8)	2935670.6200734777 iter/sec (stddev: 9.049028353180263e-9)	0.99
benchmarks/test_guard_by_type.py::test_g17_resolve_by_type_large_registry	2929499.3140015826 iter/sec (stddev: 1.7891225783950698e-8)	3112450.5020996616 iter/sec (stddev: 1.5206028604887185e-8)	1.06
benchmarks/test_guard_cold.py::test_g8_cold_first_resolve	23808.41377511408 iter/sec (stddev: 0.000006151525991179151)	23839.819437226604 iter/sec (stddev: 0.000004588540112142097)	1.00
benchmarks/test_guard_cold.py::test_g8b_cold_first_resolve_cached	18404.78696687084 iter/sec (stddev: 0.000004569674415284024)	18456.078963704393 iter/sec (stddev: 0.000004490130347246396)	1.00
benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[1]	432.22098216259195 iter/sec (stddev: 0.00005294398545290316)	435.2946231031614 iter/sec (stddev: 0.00006866699102688879)	1.01
benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[2]	413.7158856805711 iter/sec (stddev: 0.00003620620868725245)	408.9649108123275 iter/sec (stddev: 0.00007308032184575663)	0.99
benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[4]	376.34111477184973 iter/sec (stddev: 0.00003584800394370476)	348.3916838319672 iter/sec (stddev: 0.00027588481773996656)	0.93
benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[1]	2217.205548307885 iter/sec (stddev: 0.00003286376206254194)	2273.653614296736 iter/sec (stddev: 0.00002151229093875247)	1.03
benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[2]	1703.859022026382 iter/sec (stddev: 0.000034867777768477854)	1687.4341294666815 iter/sec (stddev: 0.00003796638937519399)	0.99
benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[4]	1153.8569379702524 iter/sec (stddev: 0.00004286771375870701)	1145.6557397851677 iter/sec (stddev: 0.00003435700941923532)	0.99
benchmarks/test_guard_lifecycle.py::test_g6_build_child_container	727834.5758646571 iter/sec (stddev: 4.526478663244454e-8)	757387.5725985781 iter/sec (stddev: 4.141269526957182e-8)	1.04
benchmarks/test_guard_lifecycle.py::test_g6b_build_child_container_auto_scope	682084.155882815 iter/sec (stddev: 9.138036323416977e-8)	681044.8979009917 iter/sec (stddev: 2.74365998701665e-8)	1.00
benchmarks/test_guard_lifecycle.py::test_g7_request_lifecycle_batch	2264.1707727517382 iter/sec (stddev: 0.00003989416791262109)	2335.685940782144 iter/sec (stddev: 0.000012191155130405179)	1.03
benchmarks/test_guard_lifecycle.py::test_g7c_event_loop_floor_control	57800.17601866104 iter/sec (stddev: 0.0000022986387744473665)	62052.75436745368 iter/sec (stddev: 0.00000217657442190837)	1.07
benchmarks/test_guard_lifecycle.py::test_g13_teardown_at_scale	45925.20140456258 iter/sec (stddev: 0.0000017815014821440133)	46420.765922504885 iter/sec (stddev: 0.0000021890985181612635)	1.01
benchmarks/test_guard_resolve.py::test_g1_transient_resolve	1820791.9234034019 iter/sec (stddev: 8.658155068621275e-8)	1937573.7005389982 iter/sec (stddev: 2.2326766002233246e-8)	1.06
benchmarks/test_guard_resolve.py::test_g2_cached_resolve	3284568.7642110977 iter/sec (stddev: 8.14076846546722e-9)	3221184.259857156 iter/sec (stddev: 7.956451943987457e-9)	0.98
benchmarks/test_guard_resolve.py::test_g3_deep_chain	720711.8514187422 iter/sec (stddev: 6.629135006988897e-8)	739670.6701468946 iter/sec (stddev: 3.3881894450057316e-8)	1.03
benchmarks/test_guard_resolve.py::test_g4_wide_resolve	402075.06114195986 iter/sec (stddev: 2.228002445469527e-7)	413484.39598088106 iter/sec (stddev: 8.594346413570085e-8)	1.03
benchmarks/test_guard_resolve.py::test_g5_cross_scope	1588001.3791801294 iter/sec (stddev: 2.478491543601475e-8)	1591235.0319345426 iter/sec (stddev: 2.8409447283230043e-8)	1.00
benchmarks/test_guard_resolve.py::test_g9_context_resolve	844816.3588876746 iter/sec (stddev: 4.137255398274066e-8)	851607.753436972 iter/sec (stddev: 4.2133795400223295e-8)	1.01
benchmarks/test_guard_resolve.py::test_g12_override_active_resolve	480586.21522065037 iter/sec (stddev: 6.117008189794466e-8)	495053.38942874945 iter/sec (stddev: 4.746571366710767e-8)	1.03
benchmarks/test_guard_resolve.py::test_g18_alias_hop	2267210.788185624 iter/sec (stddev: 1.403629479555219e-8)	2103271.6917714234 iter/sec (stddev: 2.385135675301081e-8)	0.93
benchmarks/test_guard_validate.py::test_g10_validate_deep_chain	27658.656298674017 iter/sec (stddev: 0.000003804398973673808)	27811.285482017563 iter/sec (stddev: 0.0000037031362964937077)	1.01
benchmarks/test_guard_validate.py::test_g11_validate_wide	17184.78733657603 iter/sec (stddev: 0.0000059491180922012215)	17259.77038836002 iter/sec (stddev: 0.000005341312985304498)	1.00

This comment was automatically generated by workflow using github-action-benchmark.

[lesnik512]

Force-pushed after a rebase onto main. The branch had been cut from a HEAD that already carried docs: drop the local PR template, inheriting the org default, so it was carrying a superseded draft of a change that has since merged to main in its final form. That commit is dropped; the branch is now main plus the single overrides/main.html commit. Re-verified against the new main: mkdocs build --strict on both sides, output diffed recursively, identical.