Download a model onto the machine that will serve it

The Models tab was about this backend's own disk, which is the wrong disk
for every session that runs anywhere else: llama.cpp reads the file where
it runs. So the models of a machine live under that machine's llama.cpp
provider now, beside the settings deciding how each is loaded, and the
download that produces one happens there.

A download is a detached `curl` on that machine, started by a script this
server writes and never spoken to again. Its state is a file beside the
partial, so nothing about it is held here: it survives the app closing,
this backend restarting and a second device watching, and the progress is
`wc -c` of the partial against the size HuggingFace published rather than
anything remembered. A run whose process is gone is reported failed, since
`kill -0` is asked at each listing, and there is no "finished" state -- a
download that finished is a model, in the list beside the ones still
going. Resuming is guarded by the published sha256, which is also checked
before the file takes its real name.

Two other things the same screens wanted:

A provider is drawn as a card rather than as a line of text, bordered
against the machine card it sits in -- the tint it had was one step along
the surface ladder and rendered as one flat block -- with room to tap and
no chevron.

Nothing in a raw block wraps any more; the block scrolls sideways
instead, one offset for all its lines, so a diff or a column-aligned test
run still reads as one.

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

server/src/main.rs

@@ -175,7 +175,6 @@ async fn main() -> Result<()> {
     let models_dir = args
         .models_dir
         .unwrap_or_else(|| data_home("ai-app").join("models"));
-    let models = Arc::new(models::ModelStore::new(models_dir.clone()));
     let manager = Arc::new(
         SessionManager::new(config_path.clone(), data_dir, models_dir.clone())
             .with_context(|| format!("failed to load {}", config_path.display()))?
@@ -290,7 +289,6 @@ async fn main() -> Result<()> {
             Arc::clone(&provider_logins),
             Arc::clone(&manager),
         ))
-        .merge(routes::models_router(Arc::clone(&models)))
         .layer(axum::middleware::from_fn_with_state(
             Arc::clone(&manager),
             auth::require_token,