feat(cmf): auto-detect tool support of managed local servers

cortiq serve >=0.5.62 advertises the loaded model's capabilities in
/healthz ({"capabilities":{"tools":true}} when the chat template has a
tools branch). The gateway now reads that handshake when the managed
server becomes healthy and treats detected tool support as equivalent
to declared caps in the candidate filter — so a low-tier chain made of
a local model no longer widens agent (tools) traffic to cloud models
once the local server can actually drive tools.

Also adds an optional manual "caps" override to [[cmf.servers]] for
older serve builds that do not advertise capabilities.

src/config.rs

@@ -130,6 +130,10 @@ pub struct CmfServer {
     /// Disable Multi-Token Prediction speculative decoding (CMF_MTP=0).
     #[serde(default)]
     pub skip_mtp: bool,
+    /// Manual capability override (e.g. ["tools"]). Usually unnecessary: the
+    /// gateway auto-detects tool support from the server's healthz handshake.
+    #[serde(default)]
+    pub caps: Vec<String>,
 }
 
 /// CMF-format model factory: import a HuggingFace model, convert it to a
@@ -229,6 +233,7 @@ impl CmfCfg {
                 o1_window: None,
                 o1_sink: None,
                 skip_mtp: false,
+                caps: Vec::new(),
             }];
         }
         Vec::new()