refactor(web): two panels on the left, the work on the right

Four panels became three, and the arrangement carries the change: everything
that organises or configures is stacked in one narrow column, and the whole of
the rest is one surface for looking at images.

Collections is a LIST, not a grid of covers — it sits in a narrow column beside
the gallery, where two cards per row meant four collections visible. A row is a
name, a count, and rename/delete on hover. Create is a dialog rather than an
always-present input, and a filter field replaces it in that space, since
finding one is the frequent act and making one is not.

Selecting a collection now shows it in the GALLERY. It used to replace the list
inside its own panel, which meant the selector disappeared the moment it was
used, and both panels kept their own copy of one collection's images and
disagreed after any edit. `?collection=` is read by the gallery now; the
collections hook stopped fetching detail entirely.

Deleting asks the question that cannot be undone: keep the images, or delete
them too. That needed a server route — DELETE /collections/:id?images=delete —
which reads the members BEFORE the collection goes, since deleting it takes the
memberships with it. Unchecked by default: the recoverable answer is the one
you get by pressing Enter without reading.

Providers stopped being a panel. It was a card per provider, each with a key
field and three buttons, filling a quarter of the screen for something set once
— it is a dropdown at the top of Generate now, listing "adapter · model" with a
delete on each, and adding one opens a dialog. The form and the dropdown share
one provider list (useProviders); they were two fetches, so adding a provider
left the form showing the old models until a reload.

sidecar/db/generations/queries.ts

@@ -20,6 +20,18 @@ export async function listGenerations(limit = 50): Promise<Generation[]> {
   return db.select().from(generations).orderBy(desc(generations.createdAt)).limit(limit);
 }
 
+/**
+ * Delete generations outright, returning the rows that went — the caller needs `image_path` to unlink
+ * the files, and after the delete there is nowhere left to read it from.
+ *
+ * `collection_items` rows go with them by foreign key, so an image deleted while filed in three
+ * collections leaves none of the three holding a dangling membership.
+ */
+export async function deleteGenerations(ids: string[]): Promise<Generation[]> {
+  if (ids.length === 0) return [];
+  return db.delete(generations).where(inArray(generations.id, ids)).returning();
+}
+
 /** Every image of one request, in the order it was asked for. This is what polling a job reads. */
 export async function getRequest(requestId: string): Promise<Generation[]> {
   return db.select().from(generations).where(eq(generations.requestId, requestId)).orderBy(asc(generations.index));