[BF-030] OG/Twitter Card 与工具页分享图

[baixiangcpp]

Issue

Closes #54

Scope

• Add localized default OG images for non-tool pages.
• Regenerate localized tool share images from the tool registry and locale catalogs.
• Route homepage, static pages, hub pages, and content pages to locale-aware default OG/Twitter images.
• Strengthen the OG image gate to verify expected coverage, dimensions, byte budget, and stale image cleanup.

Implementation

• Extended the OG generator to emit 7 default cards plus 861 canonical localized tool cards.
• Localized the card badge/tagline copy for en, zh-CN, zh-TW, ja, ko, de, and fr.
• Deleted 35 stale legacy share images that no longer map to canonical tool registry entries.
• Updated metadata helpers and app layouts so default social cards use /og/default/{locale}.jpg and tool pages keep /og/tools/{locale}/{slug}.jpg.
• Added tests for default image existence/dimensions, representative localized tool images, stale image gate execution, and locale-aware metadata.

Acceptance Criteria

• 核心页面有完整 OG/Twitter metadata。
• 工具页分享图存在并尺寸正确。
• 新增页面有默认分享图策略。
• npm run check:og-tool-images 通过。
• npm run validate 通过。
• npm run build 通过。

Validation

• npm run lint - PASS
• npm run test - PASS, 218 files / 1092 tests
• npm run validate - PASS
• npm run build - PASS
• npm run test:e2e:smoke - PASS
• npm run check:og-tool-images - PASS, 868 localized OG image(s), all 1200x630
• npm test -- tests/guards/og-tool-images.test.ts tests/guards/seo-metadata-keywords.test.ts - PASS, 9 tests
• npm test -- tests/guards/static-page-metadata.test.ts tests/guards/og-tool-images.test.ts tests/guards/seo-metadata-keywords.test.ts - PASS, 13 tests

Manual Checks

• Verified issue [BF-030] OG/Twitter Card 与工具页分享图 #54 is open before starting this PR.
• Confirmed no existing BF-030 PR was open before creating this one.
• Visually inspected public/og/default/zh-CN.jpg and public/og/tools/de/json-formatter.jpg.
• Checked built HTML contains locale-aware social image URLs for /, /fr/install-app, /zh-CN/trust-center, /en/json-formatter, and /de/json-formatter.

Privacy Check

• 不采集工具输入
• 不采集工具输出
• 不新增未披露的外部请求
• 不持久化敏感 payload
• Share images are generated only from checked-in site copy, registry data, and locale catalogs.
• No analytics payloads, query text, full URLs, file names, tokens, JWTs, secrets, logs, image contents, or generated output were added.

Screenshots / Evidence

• public/og/default/zh-CN.jpg
• public/og/default/fr.jpg
• public/og/tools/en/json-formatter.jpg
• public/og/tools/de/json-formatter.jpg
• npm run generate:og-tool-images reported: generated 868 localized OG image(s), removed 35 stale image(s).

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