[codex] Add public mobile API compatibility routes

[BunsDev]

Summary

• Add /api/public/v1/* read routes expected by the Feedback mobile SDK for posts, boards, comments, changelog, and help content.
• Map those routes onto the existing public domain/query services and preserve the SDK envelope shapes.
• Add board ID filtering to the public post query path so boardId works for /api/public/v1/posts.

Root Cause

The deployed backend and current main only exposed the authenticated /api/v1/* API plus portal/server-function paths. The iOS SDK calls /api/public/v1/*, so https://feedback.opencoven.ai/api/public/v1/posts returned the web app 404 HTML instead of JSON.

Test Plan

• git diff --check
• bunx vitest run apps/web/src/routes/api/public/v1/posts/__tests__/index.test.ts apps/web/src/routes/api/public/v1/boards/__tests__/index.test.ts 'apps/web/src/routes/api/public/v1/posts/__tests__/$postId.test.ts' 'apps/web/src/routes/api/public/v1/posts/__tests__/$postId.comments.test.ts' apps/web/src/routes/api/public/v1/changelog/__tests__/index.test.ts apps/web/src/routes/api/public/v1/help/__tests__/categories.test.ts 'apps/web/src/routes/api/public/v1/help/articles/__tests__/$slug.test.ts'
• bunx eslint apps/web/src/lib/server/domains/posts/post.public.ts apps/web/src/routes/api/public/v1/posts/index.ts 'apps/web/src/routes/api/public/v1/posts/$postId.ts' 'apps/web/src/routes/api/public/v1/posts/$postId.comments.ts' apps/web/src/routes/api/public/v1/boards/index.ts apps/web/src/routes/api/public/v1/changelog/index.ts apps/web/src/routes/api/public/v1/help/categories.ts 'apps/web/src/routes/api/public/v1/help/articles/$slug.ts' apps/web/src/routes/api/public/v1/posts/__tests__/index.test.ts 'apps/web/src/routes/api/public/v1/posts/__tests__/$postId.test.ts' 'apps/web/src/routes/api/public/v1/posts/__tests__/$postId.comments.test.ts' apps/web/src/routes/api/public/v1/boards/__tests__/index.test.ts apps/web/src/routes/api/public/v1/changelog/__tests__/index.test.ts apps/web/src/routes/api/public/v1/help/__tests__/categories.test.ts 'apps/web/src/routes/api/public/v1/help/articles/__tests__/$slug.test.ts'
• bun run typecheck
• bun run build

Deployment Note

After merge, Railway needs to redeploy feedback.opencoven.ai. Then verify https://feedback.opencoven.ai/api/public/v1/posts returns JSON instead of the web app 404 HTML.

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