[cbaucom]

Closes #16

Summary

Adds a pure importDroppedMediaFiles module in project-store that validates file types before writing, auto-suffixes duplicate filenames (photo-1.jpg), and returns imported slides plus skipped entries. The editor shell wires window drag-and-drop when a folder is open: imported media appends to the storyboard grid and unsupported types show a dismissible amber notice.

Acceptance criteria

• Given dropped media files, when the copy completes, then the files exist in the folder and appear at the end of the grid.
• Given a dropped file whose name already exists, when imported, then it is saved under a suffixed name and both remain playable.
• Given an unsupported file type, when dropped, then it is skipped with a visible notice and no partial writes remain.

Test plan

• pnpm test — import-media unit tests cover all three acceptance criteria
• pnpm build && pnpm lint
• Playwright smoke (node scripts/playwright-issue-16-smoke.mjs) — drop batch adds imported.jpg, suffixes duplicate to photo-1.jpg, shows notice for notes.txt (see issue-16-drag-drop-import.png)

Code review

Score: 5/5 — APPROVE

No blocking findings. Pure import logic lives in project-store with in-memory FS fakes; editor shell stays thin (DropImportLayer + useProject.importDroppedFiles).

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