[BF-025] 性能预算和 bundle guard

[baixiangcpp]

Issue

Closes #45

Scope

• Adds the BF-025 performance budget gate only.
• Keeps the existing heavy dependency boundary guard in place.
• Adds documentation for how and when to update route budgets.

Implementation

• Added scripts/gates/check-performance-budget.js with config validation and build-output report modes.
• Added scripts/gates/performance-budgets.json with baseline budgets for /, /en, /en/all-tools, /en/json-formatter, /en/markdown-preview, and /en/image-resizer.
• Wired npm run check:performance-budget into npm run validate.
• Wired npm run check:performance-budget:report into npm run build:post so CI prints and enforces the bundle summary after export.
• Added docs/performance/performance-budget.md and guard tests for CI wiring.

Validation

• npm run lint
  • PASS
• npm run test
  • PASS: 218 files / 1091 tests
• npm run validate
  • PASS, including check:performance-budget
• npm run build
  • PASS: 1289 static pages; check:performance-budget:report passed in build:post
• npm run test:e2e:smoke
  • PASS via npm run test:e2e:smoke -- --port=4179
• npm run analyze
  • PASS exit code 0; generated .next/analyze/client.html, .next/analyze/nodejs.html, .next/analyze/edge.html
  • Analyzer printed server/edge parse warnings but completed successfully.
• npm run check:bundle-boundaries
  • PASS: heavy dependencies stay behind approved lazy boundaries.

Bundle Budget Evidence

npm run check:performance-budget:report output from the successful build:

Route	JS gzip	JS raw	Scripts	CSS gzip	HTML
/	187.2 KiB / 214.8 KiB	627.3 KiB / 703.1 KiB	10 / 12	26.3 KiB / 34.2 KiB	63.7 KiB / 87.9 KiB
/en	220.2 KiB / 249.0 KiB	788.3 KiB / 878.9 KiB	15 / 17	26.3 KiB / 34.2 KiB	295.7 KiB / 351.6 KiB
/en/all-tools	243.4 KiB / 278.3 KiB	890.6 KiB / 1001.0 KiB	18 / 20	26.3 KiB / 34.2 KiB	522.2 KiB / 605.5 KiB
/en/json-formatter	299.5 KiB / 341.8 KiB	1061.1 KiB / 1191.4 KiB	24 / 27	26.3 KiB / 34.2 KiB	249.5 KiB / 312.5 KiB
/en/markdown-preview	251.6 KiB / 293.0 KiB	907.4 KiB / 1035.2 KiB	20 / 23	26.3 KiB / 34.2 KiB	234.9 KiB / 293.0 KiB
/en/image-resizer	290.2 KiB / 332.0 KiB	1031.3 KiB / 1152.3 KiB	24 / 27	26.3 KiB / 34.2 KiB	240.2 KiB / 302.7 KiB

Acceptance Criteria

• CI 输出 bundle 体积摘要。
• 超过预算时失败或要求显式 override。
• 核心页面有基线。
• 文档说明如何更新预算。
• npm run validate 和 npm run build 通过。

Manual Checks

• Confirmed the budget report reads exported out/ HTML and _next/static assets.
• Confirmed the budget config is not an unlimited threshold and current main stays within limits.
• Smoke test confirmed critical routes still render and navigate.

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
• 不新增 analytics payload/query/file-name collection

Screenshots / Evidence

• Non-UI CI/performance gate change; bundle report above is the evidence.

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