Add tag clouds to workspace / nested workspace / project detail pages

[netclectic]

Summary

Tags are currently only visible on individual memory entries. Add a tag cloud to the workspace, nested-workspace, and project detail pages so users can see the tag landscape at each organizational level and drill into tag-filtered memory lists.

Scope

Per the tag-cloud scope decision, a workspace tag cloud aggregates tags from the entire workspace subtree: direct workspace memories + all projects + all nested workspaces (recursive).

Changes

Backend

• New ITagCloudService / TagCloudService (auto-registered via [AutoRegisterInterfaces]), depending on NpgsqlDataSource — does not extend IStorage, so no test-fake churn.
  • GetWorkspaceSubtreeTagCountsAsync(WorkspaceId) — recursive CTE over workspaces.parent_id, unnest(tags), owner_type = 0 (workspace) / owner_type = 1 (project).
  • GetProjectTagCountsAsync(ProjectId) — direct project memories.
• New model TagCount { string Tag; int Count }.
• New endpoint GET /api/memory/tags/cloud?workspaceId=&projectId= (mutually exclusive → 400) returning [{tag, count}], sorted by count desc then tag.

Frontend

• Tag-cloud card on WorkspaceDetail.cshtml and ProjectDetail.cshtml.
• Tags rendered as clickable badges with font-size scaled by count (min ~0.8rem → max ~1.5rem); click navigates to /memories?workspaceId=X&tag=Y (or projectId).
• Section hidden when empty.
• Tag-cloud JS kept self-contained (loadTagCloud() + its own section div) so the diff stays separable from Add tag clouds to workspace / nested workspace / project detail pages #2.
• Light + dark theme styles in site.css (per project convention, [data-theme="dark"]).

Files

• New: src/Memorizer/Services/ITagCloudService.cs, Services/TagCloudService.cs, Models/TagCount.cs
• Modified: src/Memorizer/Controllers/MemoryController.cs, Views/Home/WorkspaceDetail.cshtml, Views/Home/ProjectDetail.cshtml, wwwroot/css/site.css

Notes

• Depends on Hide empty Nested Workspaces / Projects sections and move create buttons to toolbar #1 (implementation sequence; both ship in the same upstream PR).

[netclectic]

Implemented on branch feature/workspace-page (pushed to this fork).

• New ITagCloudService / TagCloudService (auto-registered, does not extend IStorage) with:
  • GetWorkspaceSubtreeTagCountsAsync (recursive CTE: direct + projects + nested workspaces)
  • GetProjectTagCountsAsync
  • GetGlobalTagCountsAsync
• New endpoint GET /api/memory/tags/cloud?workspaceId=&projectId= (global when unscoped).
• Tag cloud cards on workspace and project detail pages ("Tags" header), tags sized by count, links go to the global /memories?tag=X (no location scoping).
• Top-level "Tags" section in the sidebar — collapsible, renders as wrapping pills with counts (top 30 + "View all"), backed by the global counts endpoint.
• Tag clouds on detail pages are limited to the top 30 with a "Show all N tags" / "Show fewer" toggle.
• Light + dark theme styles for all tag cloud UI.

Follow-up refinements applied after review: renamed header to "Tags", global tag links, pill-style sidebar tags, top-30 limit.

This ships together with #1 in the same upstream PR (feature/workspace-page). Tests: 195 unit + 188 integration pass on the branch (includes tag-cloud aggregation integration tests).