Add workspace context source workbench

[mimeding]

Summary

• Adds a metadata-only inventory for context sources from memory, agent database records, sandbox context, uploaded files, workspace knowledge, and citations.
• Separates ownership, provenance, freshness, duplicate grouping, and per-agent enablement without reading payload contents.
• Adds presenter summaries for effective sources, blocked sources, warnings, and stale/malformed citation states.

Validation

• swift test --package-path Packages/OsaurusCore --filter WorkspaceContextSourceWorkbenchTests
• swiftlint lint --quiet Packages/OsaurusCore/Models/Workspace/ContextSource/WorkspaceContextSourceModels.swift Packages/OsaurusCore/Services/Workspace/WorkspaceContextSourceWorkbench.swift Packages/OsaurusCore/Services/Workspace/WorkspaceContextSourceWorkbenchPresenter.swift Packages/OsaurusCore/Tests/Workspace/WorkspaceContextSourceWorkbenchTests.swift
• git diff --check
• External review pass completed; actionable findings were incorporated before publication.
• GitHub checks are green.

Notes

• Ready for review as the boundary model for context sources. This intentionally avoids merging memory, agent database, sandbox, and workspace knowledge into one hidden context path.