fix(uploads): count a Bunny upload from the moment it is admitted

A Bunny init asked the quota whether it could store zero bytes, which is a
question with only one answer. Nothing an upload was about to consume was
visible to the next request, so every init inside the same window read the
same total and every one of them passed, and an upload that could never
fit was only refused after it had been sent.

The client now declares the size up front. It is checked against the
account's remaining room before Bunny is asked for anything, and held as
a reservation the next init has to see. The declaration is a claim rather
than proof, so it is signed into the upload token: the same token already
binds the video id, which is what makes the reservation safe to release
on a caller's say-so, since releasing it costs them the video it belongs
to.

The declared size is then written onto the version or asset row and the
reservation is dropped in the same transaction, because Bunny reports no
size at all for a video until it has finished encoding it. On a half hour
of footage that is most of an hour during which the upload did not appear
on the uploader's own storage page and did not count against the next
upload. Per-video accounting now takes the larger of what Bunny reports
and what was declared, so the estimate stands in until the real figure
arrives and Bunny's wins once it does.

Two smaller things came out of the same reading. The asset route's
in-transaction fallback compared against the plan limit, so a caller
quoting a reservation that no longer existed was measured against 200 GiB
even on a trial worth three. And the guest branch reserves without being
able to release early, because a guest grant is bound to our video id and
the caller's network context rather than to the Bunny video, which would
let the reservation be dropped while the upload it stands for carried on.

tests/component/hooks/use-version-actions.test.ts

@@ -419,7 +419,13 @@ describe('useVersionActions uploading a file to Bunny', () => {
 
     await createFromFile(harness);
 
-    expect(bodyOf(callsTo(BUNNY_INIT_URL, 'POST')[0])).toEqual({ title: 'my clip' });
+    // The size goes with the title: the server checks it against the quota and
+    // reserves it before Bunny is asked for anything, so an upload that cannot
+    // fit is refused here rather than after it has been sent.
+    expect(bodyOf(callsTo(BUNNY_INIT_URL, 'POST')[0])).toEqual({
+      title: 'my clip',
+      sizeBytes: '10',
+    });
     expect(tusUploads[0].options.endpoint).toBe('https://video.bunnycdn.com/tusupload');
     expect(tusUploads[0].options.headers).toEqual({
       AuthorizationSignature: 'sig',
@@ -436,7 +442,10 @@ describe('useVersionActions uploading a file to Bunny', () => {
 
     await createFromFile(harness);
 
-    expect(bodyOf(callsTo(BUNNY_INIT_URL, 'POST')[0])).toEqual({ title: 'Client cut' });
+    expect(bodyOf(callsTo(BUNNY_INIT_URL, 'POST')[0])).toEqual({
+      title: 'Client cut',
+      sizeBytes: '10',
+    });
   });
 
   it('registers the version against the Bunny embed and CDN thumbnail', async () => {