feat: pre-generate Directus image previews

Bundle extension (upload hook + API endpoint + admin module) that warms
Directus image transform cache in-process with an explicit acceptFormat,
so the generated file matches the browser's cache key byte-for-byte.

- resumable, window-aware backfill with progress + cancel
- system + custom presets, effective-format reporting, shadow warnings
- storage breakdown (previews vs originals), human-readable API fields
- diagnostics: resolve-plan prediction, per-file generate, ops ring buffer
- isolated dev/staging compose stack + deploy/rollback scripts

Verified on Directus 11.17.4: 40/40 tests, hash-match gate passed,
idempotent backfill, custom fixed-format presets, error surfacing.

dev/sync-extension.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+cd "$(dirname "$0")/.."
+
+npm run build
+
+mkdir -p dev/extension
+rm -rf dev/extension/dist
+cp -r dist dev/extension/dist
+cp package.json dev/extension/package.json
+
+echo "synced dev/extension (in place)"