feat(seed): seed-data tagging & wipe infrastructure (Pages reference)

[danielheene]

Summary

Adds a general-purpose seed-data tagging mechanism, plus a fully-built reference implementation for the Pages collection: create/wipe fixture data from the CLI or the admin panel, tagged so it can coexist with real content and be found/removed independently.

• Extends the existing GeneratorFlagsField with a seeded-dummy flag, rolled out to 12 collections (all except Users; Media collections already had the field).
• Shared, transport-agnostic seedPages/cleanPages logic (src/lib/seed/pages.ts) — the single source of truth for both callers below. cleanPages cascade-deletes the seeded media a page's hero referenced, gated by a live per-document flag re-check so a page that got its hero manually pointed at a real image never has that image deleted.
• CLI: pnpm seed:pages [-- --count N] / pnpm seed:pages:clean, synchronous, calls the shared logic directly.
• Admin panel: a "⋯" list-view action on Pages — "Seed…" opens a count-input modal, "Clean" opens a confirmation — both run async via Payload's jobs queue with live progress streamed over SSE and rendered as toasts (mirrors the existing TranslateControls.tsx/bilingualTranslateChannel pattern).

Design doc and implementation plan are local-only (docs/ is gitignored in this repo) — happy to share the content directly if useful for review.

Scope

This PR builds infrastructure + the Pages reference implementation only. The other 11 seedable collections (BlogTopics, 6 Resume collections) are explicit non-goals here, to follow later using Pages as the template.

Process notes

Built via subagent-driven development: fresh implementer + reviewer per task, human-escalated one design decision (a spec-mandated safety check in cleanPages that a plan-authoring bug had accidentally undermined — restored per your call), then a final whole-branch review (opus) that caught three cross-cutting issues no single task's review could see:

• cleanPages/seedPages didn't account for Pages' trash: true — a soft-deleted seeded page was invisible to Clean, permanently orphaning its media, and broke re-Seed's idempotency check. Fixed.
• A real (if narrow) SSE timing race: a very fast cleanPages run could complete before the client's SSE subscription opened, leaving a stuck toast and a stale list view. Fixed with a client-side timeout fallback.
• The admin-panel modal referenced CSS classes with no stylesheet defining them (would render unstyled) — never caught by typecheck, only by knowing to check for it. Added the missing stylesheet.

All three fixes independently re-reviewed and confirmed resolved. 6 Minor findings were logged but intentionally left unfixed (no auth check on the destructive server action — confirmed pre-existing pattern across every server action in this repo, not a regression; a few small robustness/consistency nits) — noted below as candidates for follow-up.

Verification

• pnpm typecheck — 0 errors
• pnpm vitest run — 617/617 passing (+12 new tests)
• pnpm build — succeeds
• CLI seed→idempotency-check→clean cycle run three times against a real dev database (Tasks 4, 9, and post-fix), each time with exact expected counts and independently-verified DB state before/after

Follow-ups (not blocking, not in this PR)

• No auth check on enqueueSeedCollection (matches every other server action in src/lib/actions/ today — a repo-wide gap, not new here, but worth a dedicated pass since this one action is destructive)
• seedCollection.ts dispatches on a bare 'pages' string rather than the CollectionSlug enum — fine for one entry, worth a lookup map once a second collection lands
• CLI --count doesn't validate a non-numeric/out-of-range value (silently seeds 0)
• A mid-loop seedPages failure can orphan an already-created hero image (tagged, so still manually findable)

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