Add memory plugin with semantic search and session planning

[chriswritescode-dev]

Summary

• Introduces @opencode-manager/memory — a new workspace package that acts as an OpenCode plugin, providing semantic memory storage and retrieval via vector embeddings (local all-MiniLM-L6-v2, OpenAI, or Voyage AI)
• Adds full backend routes + services (/memory), frontend Memories page, MemoryPluginConfig settings UI, and shared Zod schemas and types to integrate the plugin with the web UI
• Includes comprehensive test coverage across the memory package (cache, embedding, hooks, memory service, planning, setup) and refactors DB migrations to a runner-based approach

Changes

New Package: @opencode-manager/memory

• src/index.ts — Plugin entry point with setup, hooks, tools, and agents
• src/embedding/ — Local and API-based embedding providers with server-side sync
• src/storage/ — SQLite + vector store (vec) implementations with metadata queries
• src/services/ — Memory service with deduplication, session state management, embedding sync
• src/hooks/ — Keyword, session, and compaction hooks for memory lifecycle
• src/agents/ — Code agent with memory-aware context injection for code review tasks

Backend

• New /memory routes for CRUD, search, planning state, and embedding sync
• Plugin loader integration for @opencode-manager/memory
• Database migration runner with timestamped migration files

Frontend

• New Memories page with list and form dialog for managing memories
• New MemoryPluginConfig component in Settings for plugin configuration
• useMemories hook for API integration
• Updated RepoDetail to show memory plugin status

Testing

• Full test suite in packages/memory/test/ covering all major modules
• Tests for caching, embedding, hooks, memory service, session state, and setup
• Refactored test imports across backend to use vitest

Scope

116 files changed, ~11,240 insertions, ~1,226 deletions