Phase 7 slice 4b: archive surface + canvas lifecycle UI actions

[vicmaster]

Summary

The slice 2 archive flag has been invisible to viewer users since it shipped — surfacing it now closes that gap. Plus, all lifecycle operations (archive / unarchive / permanent-delete) become reachable from the viewer without an MCP client.

What lands

Sidebar

• New Archive entry below all workspaces, separated by a hairline.
• Cross-project archived-count badge; active state when on /archive.
• Folder-with-line SVG icon, visually distinct from project rows.

/archive route + renderArchivePage

• Cross-project listing of every archived canvas.
• Each card shows the source project name (since archive spans projects) and the timestamp it was archived.
• Slightly faded card opacity (0.78), full-saturate on hover — visual "this isn't part of active work" cue.
• Restore + Delete buttons overlay top-right of each card, fade in on hover. Delete prompts to confirm — irreversible.
• Empty state when nothing is archived, with a canvas_archive hint.

Detail-page toolbar

• Archive button when canvas is active; Restore button when archived (mutually exclusive).
• Delete button always present, styled with a red hover (.btn--danger).
• lifecycleAction() handler hits the JSON API and bounces back to /project/<canvas.projectId> on success. Delete confirms first.

Lifecycle API endpoints

• POST /api/canvas/:id/archive
• POST /api/canvas/:id/unarchive
• DELETE /api/canvas/:id

Thin wrappers over scene-graph.archiveCanvas / unarchiveCanvas / deleteCanvas. The underlying functions were already covered by test-workspace-mcp-tools.ts; the endpoints just expose them to the viewer's JS.

renderSidebar signature

Parameter renamed activeProjectId → active. Pass a project ID for project pages or the literal string 'archive' for the archive page. Project IDs are nanoids, so 'archive' is unambiguous.

Test plan

• npm run build clean
• npx tsx test-archive-view.ts — 27/27 pass:
  • Sidebar archive entry on project pages: link, count, not-active state
  • Archive page: title/meta, active-state on archive entry, contains only archived canvases, each card shows correct source project name, both Restore + Delete buttons per card
  • Archive empty state shows the right message + canvas_archive hint
  • Detail page: Archive/Restore buttons toggle correctly based on canvas.archived, Delete always present, lifecycleAction handler defined, Back link goes to canvas's project
  • Sidebar archive count drops dynamically after canvas_delete
• All 13 existing smokes + benchmark still pass — no regression on PRs Phase 5: responsive hint API + renderer mapping (items #1+#2) #6–25

What's next

Slice 5 (premium UI refresh) is the last Phase 7 piece. Per earlier plan, slice 5 will be dogfooded — I'll mock the new chrome inside canvas-mcp itself first, then implement against the mock. Produces a docs/viewer-refresh-mock.png as a side-effect.