feat: add Company course management and invitations

[lyyzka]

Summary

• add idempotent Course, membership, invitation, acceptance, and Study Room migrations with legacy Project backfill
• centralize Project/Course authorization across knowledge, conversations, documents, boards, calendar, Canvas, search, agents, and realtime fan-out
• add Company/Course/member/invitation APIs with archived-course read-only behavior, teacher invariants, seat-aware acceptance, audit records, and WuKongIM reconciliation
• add desktop/Electron Company & Course management, Project/Course session switching, course invite OAuth routing, and mobile Course/Study Room entry
• share an explicit production/mock Course contract with two Project/Course examples

Validation

• npm test — 269 passed
• npm run server:typecheck
• npm run typecheck
• npm run lint — passed (existing repository warnings only)
• npm run build — passed (existing chunk-size/dynamic-import warnings only)
• npm run guard:agent-os
• npm run guard:llm-tracked
• npm run guard:brand
• npm run guard:openbot-vendor
• npm run version:check
• desktop and 390px mobile browser smoke checks passed for management permissions, course/member/invitation rendering, course switching, and Study Room navigation
• npm run test:integration — skipped by the repository runner because INTEGRATION_DATABASE_URL is not configured in this workspace

Closes #63