fix(desktop): simplify toast label and improve timeline multi-selection

[ComputelessComputer]

Summary

• Simplified batch toast label text by removing count details for cleaner UX
• Enhanced timeline multi-selection with anchor-based selection behavior

Review & Testing Checklist for Human

• Test multi-selection in the timeline: select an item, then shift-click another to verify anchor selection works as expected — check edge cases like shift-clicking the same item, selecting across day boundaries, and shift-clicking with no prior anchor set
• Verify the toast label text displays correctly when batch-deleting sessions (ensure no count details appear)
• Confirm that single-click selection (without shift) still works correctly and resets the anchor as expected

Notes

Link to Devin run: https://app.devin.ai/sessions/1b9ae9acc87349e393883ca54ed961c6
Requested by: @ComputelessComputer

[netlify]

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[netlify]

✅ Deploy Preview for hyprnote canceled.

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.