Add Matter OS workspace

[user-in-search-of-a-name]

Summary

Adds an additive Matter OS workspace to Mike, inspired by Legora aOS, without replacing or moving any existing project screens.

What Changed

• Keeps /projects/:id as the existing Documents view.
• Adds a new Matter OS tab and /projects/:id/workspace route.
• Adds knowledge_entries schema, migration, backend helpers, and CRUD/link APIs for matter-scoped and personal-library knowledge.
• Adds project activity API for assistant events, chats, document versions/edits, and tabular reviews.
• Injects active matter knowledge into project chat context.
• Adds assistant knowledge tools for list, search, read, and review-only suggestions.
• Renders knowledge context and saveable knowledge suggestions in assistant messages.
• Adds the Matter OS UI with matter brief, guided legal actions, knowledge base, connected sources, agent activity, and recent outputs.

Validation

• git diff --check
• Backend tsc
• Frontend tsc --noEmit
• ESLint for ProjectMatterWorkspace and /projects/[id]/workspace/page.tsx
• next build --webpack
• Browser sanity check for /login