fix(pipeline): check HTTP status in fetch step

[Astro-Han]

Description

Normalize HTTP error handling in the pipeline fetch step. Single-request fetches now fail fast on non-ok responses, while per-item batch fetches return per-item { error } objects consistently in both browser and non-browser execution.

Behavior note: non-ok responses are no longer parsed as successful data. Single fetches throw immediately; batch fetches preserve per-item error objects instead of mixing browser/non-browser semantics.

Related issue: N/A

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Test Plan

• npx vitest run src/pipeline/steps/fetch.test.ts
• npm run typecheck
• npm test

Summary

• fail fast on non-ok responses in single-request fetch execution
• keep batch browser and non-browser fetch paths aligned with per-item { error } results
• use CliError('FETCH_ERROR') instead of bare Error for consistent CLI error rendering
• return error status from browser evaluate instead of throwing inside it (avoids CDP wrapper rewriting)
• add log.warn() for batch item failures in both browser and non-browser paths
• add regression tests covering error type, batch warnings, and non-Error stringification
• remove unrelated .worktrees/ change from .gitignore

Screenshots / Output

Not applicable.

[Astro-Han]

Updated this PR after follow-up review.

What changed:

• kept single-request fetch as fail-fast on non-ok HTTP responses
• aligned batch fetch semantics so browser and non-browser both return per-item { error } results
• normalized non-Error rejected values consistently across both batch paths
• expanded regression tests to cover browser/non-browser batch failures and primitive rejected values

Follow-up (review round 2):

• replaced bare Error with CliError('FETCH_ERROR') across all throw sites
• browser single-fetch now returns error status from evaluate and throws CliError outside
• added log.warn() for batch item failures in both browser and non-browser paths
• removed unrelated .worktrees/ from .gitignore

Validation:

• npx vitest run src/pipeline/steps/fetch.test.ts
• npm run typecheck
• npm test