Fix bulk alt text no-provider notice

[ekamran]

What?

Updates the bulk Alt Text Generation no-provider message to use an error admin notice.

Why?

When running the Media Library bulk Generate Alt Text action without a configured AI Connector, generation cannot proceed.

The existing message explained the problem, but it used a neutral info notice even though the action failed. Using an error notice makes the state clearer and better matches the severity of the issue.

How?

• Allows the bulk alt text notice helper to render either info or error notices.
• Uses an error notice when no AI provider is configured.
• Adds E2E coverage for the no-provider bulk action path.

Use of AI Tools

AI assistance: Yes
Tool(s): ChatGPT / Codex
Used for: Repository review, implementation guidance, test updates, and local verification. I reviewed the changes, tested the behavior locally, and take responsibility for the final submission.

Testing Instructions

1. Use WordPress 7.0 RC4.
2. Ensure no AI Connector API key is configured.
3. Enable AI features and the Alt Text Generation experiment.
4. Open Media Library in list view.
5. Select one or more images.
6. Choose Generate Alt Text from the bulk actions dropdown.
7. Click Apply.
8. Confirm an error notice appears explaining that an AI Connector is required.

Automated checks run locally:

• npm run lint:js -- src/experiments/alt-text-generation/bulk.ts tests/e2e/specs/experiments/alt-text-generation.spec.js
• npm run typecheck
• npm run build
• npm run test:e2e -- tests/e2e/specs/experiments/alt-text-generation.spec.js --project=chromium --grep "Bulk action shows an error notice when no provider is configured"

Screenshots or screencast

Before

No provider is configured. The bulk action cannot generate alt text, but the message appears as an info notice.

After

No provider is configured. The same message appears as an error notice.

[github-actions]

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Co-authored-by: ekamran <ekamran@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.21%. Comparing base (19ae2eb) to head (8d67c57).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #561   +/-   ##
==========================================
  Coverage      71.21%   71.21%           
  Complexity      1151     1151           
==========================================
  Files             67       67           
  Lines           5565     5565           
==========================================
  Hits            3963     3963           
  Misses          1602     1602           

Flag	Coverage Δ
unit	71.21% <ø> (ø)

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