feat: complete media usage tracking setup

[khoinguyenpham04]

What does this PR do?

Completes media usage tracking setup for new and existing sites.

• The setup wizard selects tracking by default for new sites and lets administrators opt out before continuing.
• Existing sites enable tracking from Settings → Media usage tracking after confirming that edits and other content updates are paused.
• The visible settings page advances durable setup and indexing. Closing it pauses new requests; returning resumes from saved progress.
• Each work claim handles up to 1,000 entries. Failures are isolated by collection, and projection memory is capped at 50,000 references or 16 MB before untouched work is released.
• Cloudflare Queue, the dedicated media usage Cron, and Node scheduled recovery are removed. The unrelated general Cron remains unchanged.
• Leases, retries, fencing, live-write safety, truthful coverage, collection deletion, Node support, and V1 compatibility remain intact.
• Media Library and REST API documentation describe the current setup flow and result coverage.

This PR is stacked on #2472 and should be reviewed against chore/media-usage-dev-seed-readiness.

No linked issue.

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). No messages.po changes are included.
• I have added and reviewed the user-facing changeset (if this PR changes a published package)
• New features link to an approved Discussion: not applicable; this completes the existing media usage tracking stack

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: OpenAI Codex (GPT-5.6)

Screenshots / test output

• Focused Admin, Core, and workerd/D1 suites pass.
• Core and Admin typechecks and builds pass, along with the documentation build.
• Type-aware lint, formatting, locale compilation, and git diff --check pass.
• Local browser verification covers the confirmation dialog, keyboard acknowledgement, setup, continuation, and Ready state.

---

Try this PR

Open a fresh playground →

A full working EmDash site, deployed from this branch. Each visit gets its own session-scoped sandbox: no login needed and no shared state.

_{Tracks feature/media-usage-activation-and-indexing. Updated automatically when the playground redeploys.}

[changeset-bot]

🦋 Changeset detected

Latest commit: 5c4c0aa

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

This PR includes changesets to release 17 packages

Name	Type
emdash	Minor
@emdash-cms/admin	Minor
@emdash-cms/cloudflare	Minor
@emdash-cms/sandbox-workerd	Patch
@emdash-cms/plugin-mcp-smoke	Major
@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

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

[github-actions]

Scope check

This PR changes 3,521 lines across 63 files. Large PRs are harder to review and more likely to be closed without review.
This PR spans 5 different areas (area/core, area/admin, area/docs, area/templates, area/cloudflare). Consider breaking it into smaller, focused PRs.

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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[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

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[github-actions]

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Tracked Files

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packages/admin/src/locales/en/messages.po	Source changed, localizations will be marked as outdated.

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[github-actions]

Overlapping PRs

This PR modifies files that are also changed by other open PRs:

• Speed up automatic Media Usage indexing #2539 (39 shared files)
• feat(admin): add Media Usage setup and indexing progress #2531 (32 shared files)
• fix(core): add controlled media usage activation #2445 (11 shared files)
• feat(core): built-in SMTP email transport for generic SMTP credentials #2156 (3 shared files)
• Add deployment-managed core migration primitives #2437 (3 shared files)
• feat: reference field type (storage-less edges + admin UI) #1928 (3 shared files)
• [codex] Add visual sections and public Pages preview #1206 (4 shared files)
• feat: cache purge API (object cache + native Workers Caching) #2297 (4 shared files)
• feat: gate sandboxed plugins behind Worker Loader so free-tier Cloudflare deploys work #2351 (4 shared files)
• fix(admin): lazy-load Media Library thumbnails #1827 (3 shared files)
• feat(media) Adds media drag uploads and picker metadata editing #1366 (3 shared files)
• feat(admin): core update notice in the admin dashboard (WordPress-style version banner) #1939 (3 shared files)

This may cause merge conflicts or duplicated work. A maintainer will coordinate.

[ascorbic]

This is pretty close! I have a few specific issues in the code, and one overarching thing. A lot of the wording in here is treating this like it's a product, when it's really just a setting. Calling it "Media Usage" (with title case) is confusing. I think it should be referred to as "media usage tracking" or something like that.