fix(memos-local-plugin): speed imports and stabilize overview

[hijzy]

Summary

• batch memory bundle import writes and cache native import scans to reduce UI stalls during large imports
• make memories pagination avoid expensive total counts while preserving navigation
• fix overview model cards so connected status cannot render as [object Object]

Tests

• npm run lint
• npm run build:viewer
• npx vitest run tests/unit/viewer/overview-model-status.test.ts
• npx vitest run tests/unit/server/http.test.ts
• npx vitest run tests/unit/pipeline/memory-core.test.ts -t "repairs missing and wrong-dimension imported trace embeddings"

No Python files changed, so ruff was not applicable.