fix(rate-limit): fail the shared write ceiling open and skip reads over POST

The shared write bucket threw on any SQL error, so a lock on rate_limits
answered every authenticated write with 500. It is a loop cutter, not an
access check: when the bucket cannot be read the write now goes ahead with
a warn signal. The login and other auth-surface limits call the limiter
directly and still fail closed. requireAuth now passes readOverPost to the
meter, the draft-only document assist declares it, and the three chat
routes, which meter their turns with buckets of their own, declare that
instead of being counted twice.

src/app/api/documents/inbound/[id]/chat/route.ts

@@ -71,7 +71,9 @@ type RouteParams = { params: Promise<{ id: string }> };
 
 export const POST = apiHandler(
   async (request: NextRequest, { params }: RouteParams) => {
-    const { user } = await requireAuth();
+    // Metered by the document chat's own bucket below, not the shared
+    // ceiling.
+    const { user } = await requireAuth(undefined, { writeBucket: "own" });
     const userId = user.id;
 
     const gate = await requireModuleEnabled(userId, "inboundDocuments");

src/app/api/documents/inbound/[id]/suggest/route.ts

@@ -73,7 +73,9 @@ type RouteParams = { params: Promise<{ id: string }> };
 
 export const POST = apiHandler(
   async (request: NextRequest, { params }: RouteParams) => {
-    const { user } = await requireAuth();
+    // Writes nothing (the draft goes back to the edit form), so the shared
+    // write ceiling does not count it; the document-AI bucket meters it.
+    const { user } = await requireAuth(undefined, { readOverPost: true });
 
     const gate = await requireModuleEnabled(user.id, "inboundDocuments");
     if (!gate.enabled) return gate.response;