Feature: Icon library uploader supports drag/drop + paste SVG input

[anand-testcompare]

Summary

Improve the icon library upload UX so users can add many SVGs quickly without repeatedly using the file picker.

Scope

Implement in the library editor upload section:

• Drag-and-drop upload for one or many SVG files
• Paste upload support for:
  • clipboard SVG files (image/svg+xml)
  • raw pasted SVG markup (<svg ...>...</svg>)
• Keep existing file-picker upload path working
• Support bulk uploads (20+ files in one action) with clear user feedback for partial failures

Non-goals

• URL/link-based imports (tracked separately / explicitly out of scope here)
• SVG clipping/render fixes (keep #153 as a separate bug)

Acceptance criteria

• User can drag/drop multiple .svg files into the upload area and all valid files are ingested
• User can paste valid raw SVG text and it uploads as a new icon
• User can paste clipboard SVG files and they upload
• Invalid SVGs are rejected with clear errors, without blocking valid files in the same batch
• Existing upload button behavior remains unchanged

Suggested file touchpoints

• apps/web/src/components/icon-library/svg-uploader.tsx
• apps/web/src/app/library-generator/[id]/page.tsx
• apps/web/src/lib/icon-library/svg-validate.ts (reuse validation logic)

Testing

• Extend e2e coverage for upload flows in tests/e2e/src/scenarios/unauthenticated/icon-library-generator-happy-path.ts
• Add/extend invalid upload scenario coverage in tests/e2e/src/scenarios/unauthenticated/icon-library-generator-invalid-svg.ts