feat: add queued toast notifications

[SameDesu123]

PR Checklist

• Required Checks
  • Have you added type definitions?
  • Have you tested your changes?
  • Have you checked that it won't break any existing features?

Summary

Reworks short non-blocking alerts into a queued toast notification flow with explicit severity, position settings, dedupe, and aggregation.

Related Issues

Part of the replacement split for #1486. Depends on #1491 and #1492.

Changes

• Redesigns toast presentation and adds a Display setting for notification position.
• Adds typed toast severity and metadata for call sites.
• Adds a bounded toast queue with dedupe and count aggregation.
• Migrates short success alerts to non-blocking success toasts.
• Clears loading/progress alerts before success toasts where needed.
• Removes the legacy type: 'toast' alert path after the queue is in place.

Impact

Short success feedback becomes non-blocking and queued. Blocking modal, dialog, and progress alert behavior should remain unchanged.

Additional Notes

This is PR 3 of 4. Because this is a fork-to-upstream PR, it targets main directly and currently includes earlier split commits. After #1491 and #1492 merge, this branch should be rebased onto updated upstream/main to reduce the diff to the toast changes only.

Validation:

• git diff --check upstream/main...HEAD
• pnpm check
• pnpm exec vitest run src/ts/toastQueue.test.ts src/ts/alertModel.test.ts

[SameDesu123]

Actual diff for this PR: +972 -169