v0.7.2: wire gate-trace-lines into view-chat — TDD

Gate trace lines rendered below each agent message in dim color.
Collapsed-gates state field for Tab toggle (default: visible).
Uses passepartout::gate-trace-lines for colored entries.

- channel-tui-view: view-chat renders gate-trace after message content
- channel-tui-state: :collapsed-gates field in init-state
- View tests: 29/29 (1 new state-field test)

org/channel-tui-state.org

@@ -134,7 +134,8 @@ See *tui-theme-presets* for named presets (dark, light, solarized, gruvbox).")
               :scroll-offset 0 :busy nil :cursor-pos 0
               :pending-ctrl-x nil
               :scroll-at-bottom t :scroll-notify nil
-              :streaming-text nil :url-buffer nil   ; v0.7.1
+              :streaming-text nil :url-buffer nil            ; v0.7.1
+              :collapsed-gates nil                         ; v0.7.2
               :dirty (list nil nil nil))))
 #+end_src