Split discovery into practical tool hubs

[baixiangcpp]

Summary

• Replaces the primary discovery/navigation model with 8 practical local-tool hubs: data/code formats, encoding/crypto, web/API/network, DevOps/logs, text/regex, images/SVG/CSS, generators/calculators, and social/metadata.
• Keeps legacy hub routes such as format-validate, web-api, generators-ids, and design-media resolvable to avoid breaking existing URLs.
• Updates client lookup generation, sitemap/IA baselines, localized hub copy, and route context handling.

TDD / Tests

• Added menu group assertions for the new primary hub list and legacy hub compatibility.
• Added coverage that CSS/SVG/image tools no longer fall into the generic generators bucket.

Validation

• npm test -- tests/unit/menu-groups.test.ts tests/guards/route-semantic-alignment.test.ts tests/guards/all-tools-route-guard.test.ts tests/component/layout-components.test.tsx tests/component/menu-group-hub.test.tsx tests/guards/route-context-utils.test.ts tests/guards/tool-index-check.test.js
• npm run check:i18n
• npm run check:client-tool-lookup && npm run check:tool-index && npm run check:sitemap-lastmod && npm run check:ia-stability
• npm run lint
• npm test
• npm run validate
• npm run build:app && npm run build:post
• npm run test:e2e:smoke
• git diff --check

Part of #8.

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