fix: complete v1.2.4 acceptance boundaries

[NoctilumeDev]

Purpose

Complete the v1.2.4 patch acceptance boundary: fix the development CSP/proxy defect, remediate the nanoid advisory, and add reproducible CI, Security, Pages, and Release governance.

Impact

• No database schema or M0-M8 business behavior changes.
• Development API requests now use the existing Vite same-origin proxy.
• Adds repository architecture, documentation, version, security, and release gates.
• Preserves the 2026-08-02 three-instance result as dated historical evidence rather than claiming a rerun.

Verification

• Backend: 282/282 tests, no failures/errors/skips, JaCoCo gate passed.
• Frontend: 68/68 tests, 71.47% line coverage, ESLint, production build, demo build, npm audit all passed.
• Real chain: six fixed identities, 70 page API responses, 20 concurrency scenarios/393 requests.
• Middleware: Redis and RabbitMQ available/unavailable control-variable checks passed.
• Browser/F12-equivalent: 116 routes, 456 API responses, 6,114 network responses, zero reported console/network/business/layout errors.
• Repository: architecture, documentation links, release version, and whitespace gates passed.

Checklist

• Change stays within the frozen maintenance scope.
• New behavior has focused verification.
• API, delivery metadata, and documentation are synchronized.
• No credentials, proxy configuration, or machine-specific paths are included.

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