Update "nonexistent times" appearance

[mirmirmirr]

This pr updates the nonexistent times to be lighter and have a slight pattern, cursor-not-allowed was also added for more emphasis.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: a196aa2d-5906-42b5-830b-4e6f95cbce8d

📥 Commits

Reviewing files that changed from the base of the PR and between 3ef5946 and 63bdbcb.

📒 Files selected for processing (1)

• frontend/src/features/event/grid/timeblocks/base.tsx

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📝 Walkthrough

Walkthrough

BaseTimeBlock now renders one background overlay per visible day column, spanning the full grid and applying a diagonal repeating linear gradient.

Changes

Per-day grid overlays

Layer / File(s)	Summary
Overlay cell rendering frontend/src/features/event/grid/timeblocks/base.tsx	BaseTimeBlock adds a loop that renders one full-height overlay cell per visible day with a repeating linear gradient background.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[jzgom067]

One small thing, when hovering a nonexistent timeslot it should clear the hovered timeslot. Currently, it keeps the last hovered one like the functionality we used to have.