v0.4.0: differentiator — prose for TUI-side (on-daemon-msg, status bar, add-msg)

Prose added:
- gateway-tui-main.org: Contract item 2 updated — on-daemon-msg now
  extracts :gate-trace, :rule-count, :foveal-id from daemon response
- gateway-tui-view.org: Status Bar section — explains the three
  differentiator visualizations (rule counter, focus map, gate trace),
  noting they cost 0 LLM tokens and are unique to Passepartout's
  deterministic gate architecture
- gateway-tui-model.org: Contract item 2 updated — add-msg supports
  &key gate-trace for message-attached trace rendering

org/gateway-tui-model.org

@@ -10,9 +10,9 @@ All state mutation flows through event handlers in the controller.
 
 1. (init-state): returns a fresh state plist with ~:msgs~ list,
    ~:input~ buffer, ~:dirty~ flag, ~:busy~ flag, and ~:connection~ status.
-2. (add-msg type text): appends a message to the ~:msgs~ list in
-   ~*state*~, tagged with a timestamp and type. Truncates at the
-   message buffer limit.
+2. (add-msg role content &key gate-trace): appends a message object
+   to the ~:messages~ vector (v0.3.3), tagged with timestamp, role,
+   and optional gate-trace from the daemon (v0.4.0).
 3. (queue-event ev): thread-safely enqueues an event for the
    reader loop. (drain-queue) returns and clears the queue.