fix: resolve scroll overflow on mock panels

[yepzdk]

Summary

• Fixed scroll not working on mock panels (Process Map, Dashboard, Operations, etc.)
• Root cause: body used min-height: 100vh instead of height: 100vh, allowing the flex layout to grow beyond the viewport so overflow-y: auto on panels never activated
• Changed body to fixed viewport height, added min-height: 0 on flex ancestors, removed forced min-height: 400px on process canvas
• Most panels now use display: block; only Tasks and AI Assistant use display: flex (needed for kanban board and chat stretching)

Test plan

• Process Map → scroll the process list table
• Process Map → click Parking Complaint → scroll down to see version history
• Dashboard → scroll to see full chart section on small viewports
• Operations → scroll to see alerts table
• AI Assistant → chat messages scroll within the chat container
• Agents → detail view scrolls

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