fix: improve diagram cards and persist embedded assets

[anand-testcompare]

Summary

• make diagram list cards fully clickable and include the preview inside the open-diagram link
• replace the ad hoc preview renderer with Excalidraw export rendering and add a collapsible AI sidebar
• persist Excalidraw files end to end so pasted/imported image assets survive reloads and session seeding

Validation

• bun x ultracite fix
• bun run check-types
• bun run build
• (cd packages/backend && bun run test)
• (cd packages/opencode-excalidraw && bun run typecheck)
• local browser verification on http://localhost:3001:
  • card click-through works
  • sidebar collapse/expand works
  • file-backed image element persists after reload
  • list view preview link contains the preview image

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Project	Deployment	Actions	Updated (UTC)
sketchi-web	Ready	Preview, Comment	Apr 17, 2026 4:31am

[github-actions]

Browserbase Replays

• Session 10996112-cf37-4a67-81f8-afea703691a5 (scenario: visual-sanity.ts): replay | debug
• Session 1a669047-164d-4bab-8284-131703cb3bd3 (scenario: auth-gates.ts): replay | debug
• Session e611f706-9fbc-4698-b538-2fb2d442c23b (scenario: opencode-web-continuity.ts): replay | debug
• Session 32270653-b0fc-4442-927e-7610ea90d038 (scenario: diagram-studio-happy-path.ts): replay | debug
• Session fff04786-93d3-4ced-97d4-2893e4cdae1c (scenario: diagram-studio-occ-conflict.ts): replay | debug

Workflow run: 24547752093