Let colleagues finish each other's drafts, one at a time

Seeing a colleague's draft turned out to be half a feature: the point of
sharing it is to finish it while they are away. So writing is allowed
now -- but never by two people at once.

A draft is a single JSONB field. Whoever saves writes the whole state,
not the changed field, so two open wizards overwrite each other
completely and the second person sees nothing wrong: their own state is
right there on screen. That is why writing stayed with the owner until
now, and a lock is what makes giving that up safe.

The lock lives in the row (locked_by, locked_at) and is enforced by the
update and delete policies, not by the application. It expires, and that
is the important half: releasing happens when the wizard closes, and a
closed laptop never closes a wizard. Without expiry one crashed tab
would take a draft away for good -- worse than the problem being solved.
The wizard refreshes its lock while open so a long form does not lose it
mid-way.

Delete had to widen too, which reads like more than was asked for: the
wizard deletes the draft once the person is hired. Without it the hire
would go through and the draft would sit there forever. The card still
only offers delete on your own drafts.

Four of five mutations against the lock go red. The fifth -- dropping
`!open` from the refresh guard -- does not, because freigeben() already
nulls the ref the interval checks. The condition stays as the readable
statement of intent, now with a comment saying so.

Not run against a live database here; the CI migration job is the first
real execution.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

lib/types.ts

@@ -338,9 +338,29 @@ export type Database = {
         };
         Update: Partial<Database["public"]["Tables"]["employee_notes"]["Insert"]>;
       };
+      // locked_by/locked_at: wer den Entwurf gerade offen hat. Die Regeln
+      // hire_drafts_update und _delete lassen nur den Halter schreiben, und
+      // die Sperre läuft ab (Migration 20260910160000) — sonst nähme ein
+      // geschlossener Reiter den Entwurf für immer mit.
       hire_drafts: {
-        Row: { id: string; created_by: string | null; step: number; payload: Record<string, unknown>; updated_at: string };
-        Insert: { id?: string; created_by?: string | null; step?: number; payload: Record<string, unknown>; updated_at?: string };
+        Row: {
+          id: string;
+          created_by: string | null;
+          step: number;
+          payload: Record<string, unknown>;
+          updated_at: string;
+          locked_by: string | null;
+          locked_at: string | null;
+        };
+        Insert: {
+          id?: string;
+          created_by?: string | null;
+          step?: number;
+          payload: Record<string, unknown>;
+          updated_at?: string;
+          locked_by?: string | null;
+          locked_at?: string | null;
+        };
         Update: Partial<Database["public"]["Tables"]["hire_drafts"]["Insert"]>;
       };
       saved_reports: {