feat: add VectorStore management UI settings page

[ochanism]

Overview

Add a settings page for managing VectorStore instances with full CRUD, connection testing, and dynamic form rendering from the /types API.

close #921

Changes

Frontend (frontend/src/):

• api/vector-store.ts — API wrapper (types + CRUD + test functions)
• views/settings/VectorStoreSettings.vue — Main settings component (~780 lines)
• views/settings/Settings.vue — Sidebar menu item + routing
• i18n/locales/{en-US,ko-KR,zh-CN,ru-RU}.ts — Full i18n with 51 keys per locale

Features:

• VectorStore list with env store (read-only, DEFAULT tag) and DB store separation
• Add dialog: engine type selection → dynamic connection/index fields from /types API
• Edit dialog: name only editable, immutable fields shown as read-only text + info banner
• Delete with DialogPlugin.confirm
• Connection test: inline result on cards + pre-save test in dialog
• Advanced settings: collapsible section with shard/replica scalability options
• Input bounds: shard fields (1-64), replica fields (1-10), name regex validation
• Immutable reactive state updates throughout (no direct property mutation)

Backend (minor, from UI testing feedback):

• GetVectorStoreTypes(): remove postgres/sqlite from types list, simplify display names
• BuildEnvVectorStores: clean env store names ("PostgreSQL" instead of "postgres (env)")
• scripts/dev.sh: fix go run for multi-file main package

Core

Key file: frontend/src/views/settings/VectorStoreSettings.vue

• Dynamic form rendering from /types API (connection_fields + index_fields)
• fieldLabel() helper with i18n fallback
• isReplicaField() for shard vs replica input bounds
• indexNamePattern regex validation on index/collection name fields

Screenshots

Test Plan

• Frontend build (npm run build) clean
• Go build + go test clean
• Manual testing: add/edit/delete stores, connection test, dynamic forms, i18n switching
• All 4 locales verified (en-US, ko-KR, zh-CN, ru-RU)
• Edge cases: empty state, long names, validation errors

Related

• Depends on: feat: add registry dual-map and engine factory for VectorStore #973 (PR3: Registry dual-map), feat: pass IndexConfig to repositories with scalability options #981 (PR3-2: IndexConfig + Scalability)