Fix manage sidebar appearing below content

[andreagrandi]

Summary

• The manage sidebar was rendering below the dashboard content instead of beside it on desktop
• Root cause: the <main> tag from base.html had max-w-6xl which constrained the DaisyUI drawer, preventing the sidebar and content from sitting side by side
• Added a {% block main_class %} override so manage pages use w-full flex-1 without the width constraint

Test plan

• Visit /manage/ on desktop — sidebar should appear on the left, content on the right
• Visit /manage/ on mobile — sidebar should be hidden behind hamburger toggle
• Verify public pages are unaffected (still use max-w-6xl)