feat(media) Add media drag uploads and picker metadata editing

[masonjames]

What does this PR do?

Adds the next media workflow improvements from discussion #990:

• Adds drag-and-drop batch uploads to the Media Library and Media Picker.
• Reuses the existing upload paths with shared batch progress and error handling.
• Adds active/reject drop states, upload progress, success/error messages, and invalid-file rejection.
• Keeps picker uploads selected after successful upload, including provider uploads.
• Adds inline alt text and caption editing in the Media Picker using the existing updateMedia behavior.
• Adds missing-alt, alt-set, and caption-set indicators plus quick edit affordances.

Related discussion: #990

Closes: n/a (discussion-driven feature)

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main.
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion: Make media handling a first-class editing workflow #990

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: GPT-5 Codex, RepoPrompt workflow tools

Screenshots / test output

Manual QA completed locally before PR creation; optional RTL check was not rerun manually. The implementation was also smoke-checked in Arabic/RTL during development.

Automated checks run locally:

• pnpm format
• pnpm lint:json | jq '.diagnostics | length' -> 0
• pnpm typecheck -> passed
• pnpm --filter @emdash-cms/admin test tests/components/MediaLibrary.test.tsx tests/components/MediaPickerModal.test.tsx --run -> 64 passed
• pnpm --filter @emdash-cms/admin build -> passed

[changeset-bot]

🦋 Changeset detected

Latest commit: 841dcf2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 16 packages

Name	Type
@emdash-cms/admin	Minor
emdash	Minor
@emdash-cms/cloudflare	Minor
@emdash-cms/sandbox-workerd	Patch
@emdash-cms/fixture-perf-site	Patch
@emdash-cms/perf-demo-site	Patch
@emdash-cms/cache-demo-site	Patch
@emdash-cms/do-demo-site	Patch
@emdash-cms/do-solo-demo-site	Patch
@emdash-cms/auth	Minor
@emdash-cms/blocks	Minor
@emdash-cms/gutenberg-to-portable-text	Minor
@emdash-cms/x402	Minor
create-emdash	Minor
@emdash-cms/auth-atproto	Patch
@emdash-cms/plugin-embeds	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

Scope check

This PR changes 2,259 lines across 8 files. Large PRs are harder to review and more likely to be closed without review.

If this scope is intentional, no action needed. A maintainer will review it. If not, please consider splitting this into smaller PRs.

See CONTRIBUTING.md for contribution guidelines.

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commit: 841dcf2

[masonjames]

Update 2026-06-17:

• Merged current upstream main (a436ceb8) into this branch to pick up the latest released EmDash package state (emdash@0.20.0) and clear the previous conflict state.
• Resolved the media library/picker conflicts by retaining this PR's drag-upload + metadata editing behavior while preserving upstream thumbnail fallback/dimension handling.
• PR diff against upstream main remains scoped to the media changeset and admin media files.

Local verification on 4a9df1d8:

• pnpm install --frozen-lockfile
• pnpm --filter @emdash-cms/plugin-types build (refreshes local dist for merged upstream exports)
• pnpm --filter @emdash-cms/admin test tests/components/MediaLibrary.test.tsx tests/components/MediaPickerModal.test.tsx --run -> 64 passed
• pnpm --filter @emdash-cms/admin build
• pnpm --filter @emdash-cms/admin typecheck
• pnpm lint:json | jq '.diagnostics | length' -> 0\n\nNote: the focused browser test run still prints the upstream Vitest/@vitest-browser version warning, but the tests pass after clearing stale Vite optimized-dependency caches.

[masonjames]

Follow-up after CI completed: the branch is rebased/merged onto current main and is no longer conflict-dirty. Most checks passed, including CI Typecheck, Lint, Tests, Integration Tests, Browser Tests, all E2E shards, CodeQL, zizmor, formatting, and preview publishing. The remaining red check is CI / Smoke Tests, failing in tests/integration/smoke/site-matrix-smoke.test.ts for the aggregate command pnpm run --recursive --filter {./templates/*} --filter @emdash-cms/playground build. The log does not show a media-library-specific assertion failure; it reports the aggregate template-build command failure. I tried to rerun failed jobs, but GitHub rejected it because this account does not have admin rights on the repository.