fix(memory): prefix memory routes with /api/v1 and add image preview

[enkizan]

Summary

• Fix memory page 404s by changing MemoryController route from /memory to /api/v1/memory so it matches the web client paths in packages/web/src/lib/api/memory.ts.
• Add inline image preview in the workspace: new ImagePreview component fetches the file via the workspace download endpoint with Authorization header and a new inline=true query, then renders it from an object URL.
• WorkspaceController.downloadFile accepts inline query and sets Content-Disposition: inline|attachment accordingly.
• WorkspaceService.downloadFile resolves Content-Type via an extension → MIME map (e.g. .png → image/png) instead of generic image/*, so browsers render images correctly.
• Drop the redundant close button in FullPreviewDialog (Dialog already renders one) and adjust header padding.

Test plan

• Memory page loads list, read, create, update, delete without 404.
• In workspace, clicking an image file shows inline preview in side panel and full-preview dialog.
• Non-image binary files still show the "preview not available" message.
• Downloading a non-image file still works (attachment disposition).
• workspace.controller.test.ts passes including new inline=true case.

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