Docs UX audit: fix all 53 Low findings

[lesnik512]

What

Clears every Low-severity finding from the 2026-06-13 docs UX audit (planning/audits/2026-06-13-docs-ux-audit-report.md). The 16 Mediums shipped in #212; this is the follow-up batch. Docs + four docstrings only — no behavior change.

Coverage (53 Lows)

• Onboarding / intro (O-8/9/11/12/13, X-8/13/14/15, R-2): index.md step headings restructured (## 4. parent + Option A/B), "finalizers" glossed, "Where to next" now includes Resolving + Factories, "dependency graph" grammar; about-di.md AppModule→AppGroup, singleton/scoped/transient mapped to modern-di's model, CacheSettings() glossed, import uuid; resolving.md explicit scope=, nullable-None rule; design-decisions.md "three concrete provider types".
• Provider pages (D-2/3/4/5/6/7/8/9/12/13, X-5/12): scopes.md names ScopeNotInitializedError, defines Dependencies/custom-scope MyGroup, async-vs-sync guidance; lifecycle.md imports + consistent "reverse-creation order"; factories.md reordered (Types → Parameters → Resolution behavior; anchors preserved), list[X] | None = None fix, dropped "(X-3)", "lifetime (scope)"; alias.md "a future release", overrides link; errors-and-exceptions.md troubleshooting cross-links.
• Integrations / testing (O-14/15/16/17, D-14/15/16/17/18): fastapi.md gains an ## API table + validate=True; litestar.md/typer.md unused-import + placeholder fixes (Job class); pytest.md expose attribute clarified + recipe link; fixtures.md cross-ref repointed.
• Troubleshooting / migration / contributing (X-9/16/17, D-20/22/26): context-not-set.md real missing-value rule; See also added to circular-dependency + duplicate-type-error; full error-message note; to-2.x.md empty-block SyntaxError fixed; testing-overrides.md sa_async.AsyncSession; contributing.md CI-command + subset-test tips.
• Architecture (A-1/2/4/5/6, X-10): containers.md happy-path lead + top-level Group import; providers.md populated kwargs example, bound_type notes on Alias/ContextProvider, "creator callable" terminology; testing-and-overrides.md adds the REQUEST-scoped provider its snippet uses.
• Docstrings (DS-1/2/3/4): Container + __init__, resolve/resolve_provider, Scope, ContextProvider.

D-10 was already resolved by the X-3 split in #212; R-2 and D-24 were already satisfied there (no change).

Verification

• mkdocs build --strict — exit 0, no broken-link/nav warnings; factories.md #optional-parameters/#bound_type anchors preserved.
• just lint-ci — clean (docstrings well-formed; docs/ is ruff-excluded).
• just test-ci — 199 passed, 100% coverage.
• New/changed runnable snippets executed with uv run python.

Executed via parallel file-scoped subagents (disjoint files) with central verification.

🤖 Generated with Claude Code