Add Attention sidebar section for sessions needing user input

[dhilgaertner]

Summary

• Adds a top-level Attention section at the top of the sidebar that collects sessions needing user action (permission prompt, question, or task complete)
• Sessions move out of their normal group (Active, Reviews, In Review) into the Attention section while in an attention state, and return automatically when resolved
• Section header shows an orange badge count; hidden when no sessions need attention

Test plan

• Launch app with multiple sessions
• Trigger a permission prompt in one session — verify it moves to Attention section with orange highlight and "Permission" badge
• Trigger an AskUserQuestion — verify it shows in Attention with "Question" badge
• Let a session complete (done state) — verify it appears in Attention with "Done" badge
• Resolve the attention (approve permission, answer question) — verify session returns to its normal group
• Verify the Attention section hides when no sessions need attention
• Verify search filters apply to Attention section sessions
• Verify context menus work on sessions in Attention section
• Verify ticket board still shows linked sessions when they're in Attention state

Closes #110

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