feat: replace Algolia with local CJK search

[Innei]

Summary

• replace Algolia search and config wiring with a Mongo-backed local search index
• add CJK-aware token indexing plus BM25-style reranking for unified post/note/page search
• update API client, tests, and lockfile for the local search flow

Test Plan

• pnpm -C apps/core lint
• pnpm -C apps/core typecheck
• pnpm -C apps/core exec vitest run test/src/modules/search/search.service.spec.ts test/src/modules/configs/configs.service.spec.ts test/src/modules/configs/configs.util.spec.ts
• pnpm -C packages/api-client exec vitest run tests/controllers/search.test.ts

[safedep]

SafeDep Report Summary

No dependency changes detected. Nothing to scan.

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