feat: integrate PRD 4 navigation and Command Palette

[Vonng]

Summary

Integrates the merged OINK PRD 4 theme into the bilingual consumer site:

• add Hugo-native nested Docs and Blog top navigation plus a Project product root
• exercise desktop disclosures, mobile multi-open accordions, active ancestry, flat compatibility, and deep static-group fallback
• opt into group-only sidebar icons
• configure localized safe URL and built-in Command Palette commands
• add search keywords, inherited boosts, canonical and compatibility exclusion aliases, root/type/breadcrumb assertions, and index budgets
• cover search-disabled and print runtime omission
• extend EN/ZH, root/subpath, no-JS, responsive, keyboard, focus-restoration, and axe regressions
• pin the consumer module to the merged theme main commit 9fc1d5ea50c843698cd08d31940c72bcfec45395

Closes #3

Validation

The final published-module state was tested without a local theme replacement:

• npm test passes using an isolated Go workspace and the public pseudo-version v0.2.2-0.20260812083702-9fc1d5ea50c8
• 9 Hugo build tests
• 9 alternate-site/root/subpath tests
• 18 rendered Markdown goldens
• 15 favicon tests
• translation coverage: 86/86 files and 777 headings
• rendered-link validation: 362 pages, 16,077 internal links, 2,567 fragments
• npm run test:browser: 81 passing Playwright checks (29 axe/WCAG + 52 functional)
• prior cross-version integration also passed with Hugo 0.160.1+extended and 0.164.0+extended

Runtime and privacy

• EN/ZH indexes remain language-separated and local.
• Empty and > command modes do not fetch the search index.
• Search-disabled and print builds omit Palette/index runtime.
• No default Palette telemetry or external search requests are introduced.

Depends on and now pins the merged theme PR pgsty/oink#20.

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