feat(app-dev): sync error hints, flatEntity labels, dev-mode summary UI, and docs (#21252)

Split out of #21240 — all remaining app-dev improvements. Stacked on
#21251 (review/merge that first).

- Actionable recovery hints on failed syncs; unified diff renderer;
`--dry-run` guard.
- Return `flatEntity` on update/delete sync actions and unify the diff
label.
- Summarize the dev-mode entity list unless `--verbose`.
- Docs: syncing & recovery guide + dry-run + open-an-issue prompt.
- Live execution mode for synced logic functions; clearer manifest
warnings.

<img width="1018" height="700" alt="image"
src="https://github.com/user-attachments/assets/5e9ce19e-0f1d-4f99-8524-4e118bde932b"
/>

packages/twenty-server/src/engine/workspace-manager/workspace-migration/universal-flat-entity/types/universal-flat-entity-diff.type.ts

@@ -0,0 +1,11 @@
+import { type AllMetadataName } from 'twenty-shared/metadata';
+
+import { type MetadataUniversalFlatEntity } from 'src/engine/metadata-modules/flat-entity/types/metadata-universal-flat-entity.type';
+import { type MetadataUniversalFlatEntityPropertiesToCompare } from 'src/engine/workspace-manager/workspace-migration/universal-flat-entity/types/metadata-universal-flat-entity-properties-to-compare.type';
+
+export type UniversalFlatEntityDiff<T extends AllMetadataName> = {
+  [K in MetadataUniversalFlatEntityPropertiesToCompare<T>]?: {
+    before: MetadataUniversalFlatEntity<T>[K];
+    after: MetadataUniversalFlatEntity<T>[K];
+  };
+};