refactor(host/usb): bump hsmc to 0.5 and collapse WaitingForFirstFrame into Connected

hsmc 0.5 makes default(...) optional on every state. Drop the
WaitingForFirstFrame substate that existed only because 0.4 required
Connected to declare a default child — Connected itself is now the
resting "DTR up, no traffic yet" state, and on(FrameReceived) => Active
descends into the inactivity-timer state on the first byte. Behavior is
identical (entry/exit chain math unchanged); the chart has one fewer
state and one fewer default().

Display and Radio charts left as-is — their defaults are all classic
descents serving real grouping/lifecycle purposes (Splash grouping,
Bright sub-state isolation, RX/TX session lifecycle), not 0.4 artifacts.
No journal-replay tests in this repo, so the 0.5 journal-format change
does not apply.

Cargo.toml

@@ -33,7 +33,7 @@ embassy-usb-driver = "0.2"
 ucobs = { version = "0.3", features = ["legacy-msrv"] }
 heapless = "0.9"
 donglora-protocol = "1"
-hsmc = { version = "0.4", default-features = false, features = ["embassy", "trace-defmt"] }
+hsmc = { version = "0.5", default-features = false, features = ["embassy", "trace-defmt"] }
 # Local path while iterating on CAD IRQ-clear / standby-after-CAD fixes.
 # Switch back to git fork (then crates.io) once changes are upstreamed.
 lora-phy = { path = "../../lora-rs/lora-phy", features = ["defmt-03"] }