chore(release): v0.2.8 — multiple managed local models

- The gateway can now run several local .cmf models at once: a [[cmf.servers]]
  list, one supervised `cortiq serve` per entry on its own port, each registered
  in the pool and independently routable/pinnable. The single legacy
  local_model/local_port still works (back-compat via effective_servers()).
- Settings → Local models is now a rows editor (id · path · port + check · threads
  · GPU) with add/remove and per-server serving status.
- Deleting a managed model stops just its server and removes its file — unless
  another model still points at the same file (shared-file guard).

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cortiq-gateway"
-version = "0.2.7"
+version = "0.2.8"
 edition = "2021"
 rust-version = "1.75"
 license = "Apache-2.0"