feat(review): support multi-repo workspace reviews

[Oscar-Silva]

Summary

• add workspace review support so Plannotator can review multiple nested repos from a non-git parent directory in one session
• make review state repo-aware end-to-end, including diff switching, file-content lookup, staging, PR actions, viewed state, and agent path routing
• add in-app workspace repo controls plus regression coverage for workspace discovery, duplicate repo-relative paths, export/file tree/search behavior, and non-git workspace root detection

Closes #527

Test plan

• bun test packages/server/review-workspace.test.ts packages/server/vcs.test.ts packages/review-editor/utils/exportFeedback.workspace.test.ts packages/review-editor/utils/buildFileTree.workspace.test.ts packages/review-editor/utils/reviewSearch.workspace.test.ts
• bun run --cwd apps/review build && bun run build:hook && bun run build:opencode
• Manual OpenCode workspace review from a non-git parent directory with multiple nested repos
• Verify repo selector appears in the review UI and repos with local changes are selected by default
• Verify repo-specific diff switching and workspace review feedback work correctly